修改MAC的hostname

在中文版的 Mac OS裡，系統會自動依照安裝時給的中文姓名翻譯成英文作為主機名稱。對我來說因為常常會用shell底下操作，就超想改hostname，方法如下：
直接編輯"系統偏好設定"/"共享"/"電腦名稱"即可，後面的".local"不用理他。


打開終端機之後就可以看到hostname修改好了。

參考資料：
1. 更改 Mac 主機名稱

Linux Kernel（16.1）- Network Device Driver, simple snull.

這一篇藉由LDD(Linux Device Drivers)中的SNULL來了解最基本的Network Device Driver的架構，本章的sample code比原本的SNULL更為簡化，但是Network Topology是相同的，讓interface sn0/sn1可以透過遠方虛擬的remote0/remote1彼此溝通。

最基本的Network Device Driver的寫法就是allocate network device, "struct net_device"並且賦予hook function, "struct net_device_ops"，然後將該network device註冊到kernel中，Kernel就可以調用該Network device，最基本的net_device_ops包含

• ndo_open() and ndo_validate_addr() are called, when the NIC is bring up.
• ndo_stop() is called, when the NIC is shut down.
• ndo_start_xmit() is called, when a packet is sent from the NIC.
• ndo_change_mtu() is called, when the MTU of the NIC is changed.
• ndo_set_mac_address() is called, when the MAC address of the NIC is changed.

以下是demo code的net_device_ops部分

static const struct net_device_ops nic_netdev_ops = {
    /* Kernel calls ndo_open() and ndo_validate_addr()
     * when you bring up the NIC
     */
    .ndo_open               = nic_open,
    .ndo_validate_addr      = nic_validate_addr,

    /* when you shut down the NIC, kernel call the .ndo_stop() */
    .ndo_stop               = nic_close,

    /* Kernel calls ndo_start_xmit() when it wants to 
     *   transmit a packet. 
     */
    .ndo_start_xmit         = nic_start_xmit,

    /* ndo_change_mtu() is called, when you change MTU */
    .ndo_change_mtu         = nic_change_mtu,

    /* ndo_set_mac_address() is called,
     *   when you change the MAC addr
     */
    .ndo_set_mac_address    = nic_set_mac_addr,
};

我們是模擬ethernet，而ethernet有一些hook function可以用，如下

• ndo_validate_addr() -> eth_validate_addr().
• ndo_change_mtu() -> eth_change_mtu().
• ndo_set_mac_address() -> eth_mac_addr().

在demo code中，ndo_validate_addr()/ndo_change_mtu()/ndo_set_mac_address()我都是將其轉成ethernet的default hook function，我沒直接掛，是因為我想印出訊息來看

static int nic_validate_addr(struct net_device *netdev)
{
    struct nic_priv *priv = netdev_priv(netdev);
    netif_info(priv, drv, netdev, "%s(#%d), priv:%p\n",
                __func__, __LINE__, priv);
    return eth_validate_addr(netdev);
}

static int nic_change_mtu(struct net_device *netdev, int new_mtu)
{
    struct nic_priv *priv = netdev_priv(netdev);
    netif_info(priv, drv, netdev, "%s(#%d), priv:%p\n",
                __func__, __LINE__, priv);
    return eth_change_mtu(netdev, new_mtu);
}

static int nic_set_mac_addr(struct net_device *netdev, void *addr)
{
    struct nic_priv *priv = netdev_priv(netdev);
    netif_info(priv, drv, netdev, "%s(#%d), priv:%p\n",
                __func__, __LINE__, priv);
    return eth_mac_addr(netdev, addr);
}

另外幾個比較重要的function是netif_start_queue()/netif_stop_queue()

• netif_start_queue()是通知上層，可以將資料送到該網卡，通常放在ndo_open()裡面
• netif_stop_queue()是通知上層，停止將資料送到該網卡，通常放在ndo_stop()裡面

由於我們沒有真的remote0/remote1可以回應，所以必須設定flag/IFF_NOARP在sn0跟sn1，並且自己要處理L2的header，所以必須在額外掛上"struct header_ops"。

以下為完整的driver，主要code都是印訊息觀察driver的call flow

/* reference ldd3, snull.c */
#include <linux/module.h>
#include <linux/netdevice.h>
#include <linux/etherdevice.h>

/* for in_device, in_ifaddr */
#include <linux/inetdevice.h>

MODULE_AUTHOR("Brook");
MODULE_DESCRIPTION("Kernel module for demo");
MODULE_LICENSE("GPL");

#define MAX_ETH_FRAME_SIZE   1792
struct nic_priv {
    /* you can use array to queue more packet */
    unsigned char *tx_buf;
    unsigned int  tx_len;
    u32           msg_enable;
};

static struct net_device *nic_dev[2];
/* netif msg type, defined in netdevice.h
    NETIF_MSG_DRV           = 0x0001,
    NETIF_MSG_PROBE         = 0x0002,
    NETIF_MSG_LINK          = 0x0004,
    NETIF_MSG_TIMER         = 0x0008,
    NETIF_MSG_IFDOWN        = 0x0010,
    NETIF_MSG_IFUP          = 0x0020,
    NETIF_MSG_RX_ERR        = 0x0040,
    NETIF_MSG_TX_ERR        = 0x0080,
    NETIF_MSG_TX_QUEUED     = 0x0100,
    NETIF_MSG_INTR          = 0x0200,
    NETIF_MSG_TX_DONE       = 0x0400,
    NETIF_MSG_RX_STATUS     = 0x0800,
    NETIF_MSG_PKTDATA       = 0x1000,
    NETIF_MSG_HW            = 0x2000,
    NETIF_MSG_WOL           = 0x4000,
*/
#define DEF_MSG_ENABLE 0xffff

static void dump(unsigned char *buf)
{
    unsigned char *p, sbuf[2*(sizeof(struct ethhdr) + sizeof(struct iphdr))];
    int i;
    p = sbuf;

    for(i = 0; i < sizeof(struct ethhdr); i++) {
        p += sprintf(p, "%02X ", buf[i]);
    }
    printk("eth %s\n", sbuf);

    p = sbuf;
    for(i = 0; i < sizeof(struct iphdr); i++) {
        p += sprintf(p, "%02X ", buf[sizeof(struct ethhdr) + i]);
    }
    printk("iph %s\n", sbuf);

    p = sbuf;
    for(i = 0; i < 4; i++) {
        p += sprintf(p, "%02X ", buf[sizeof(struct ethhdr) + sizeof(struct iphdr) + i]);
    }
    printk("payload %s\n", sbuf);
}


static void
nic_rx(struct net_device *netdev, int len, unsigned char *buf)
{
    struct sk_buff *skb;
    struct nic_priv *priv = netdev_priv(netdev);

    netif_info(priv, hw, netdev, "%s(#%d), rx:%d\n",
                __func__, __LINE__, len);
    /*
     * The packet has been retrieved from the transmission
     * medium. Build an skb around it, so upper layers can handle it
     */
    skb = dev_alloc_skb(len + 2);
    if (!skb) {
        netif_err(priv, rx_err, netdev,
                  "%s(#%d), rx: low on mem - packet dropped\n",
                  __func__, __LINE__);
        netdev->stats.rx_dropped++;
        return;
    }
    skb_reserve(skb, 2); /* align IP on 16B boundary */
    memcpy(skb_put(skb, len), buf, len);

    /* Write metadata, and then pass to the receive level */
    skb->dev = netdev;
    skb->protocol = eth_type_trans(skb, netdev);
    skb->ip_summed = CHECKSUM_UNNECESSARY; /* don't check it */
    netdev->stats.rx_packets++;
    netdev->stats.rx_bytes += len;
    netif_rx(skb);
}

static int nic_open(struct net_device *netdev)
{
    struct nic_priv *priv = netdev_priv(netdev);
    netif_info(priv, ifup, netdev, "%s(#%d), priv:%p\n",
                __func__, __LINE__, priv);
    /* may be using DMA */
    priv->tx_buf = kmalloc(MAX_ETH_FRAME_SIZE, GFP_KERNEL);
    if (priv->tx_buf == NULL) {
        netif_info(priv, ifup, netdev, "%s(#%d), cannot alloc tx buf\n",
                    __func__, __LINE__);
        return -ENOMEM;
    }
    netif_start_queue(netdev);
    return 0;
}

static int nic_close(struct net_device *netdev)
{
    struct nic_priv *priv = netdev_priv(netdev);
    netif_info(priv, ifdown, netdev, "%s(#%d), priv:%p\n",
                __func__, __LINE__, priv);
    netif_stop_queue(netdev);
    return 0;
}

static void nic_hw_xmit(struct net_device *netdev)
{
    struct nic_priv *priv = netdev_priv(netdev);
    struct iphdr *iph;
    u32 *saddr, *daddr;
    struct in_device* in_dev;
    struct in_ifaddr* if_info;

    if (priv->tx_len < sizeof(struct ethhdr) + sizeof(struct iphdr)) {
        netif_info(priv, hw, netdev, "%s(#%d), too short\n",
                   __func__, __LINE__);
        return;
    }
    dump(priv->tx_buf);
    iph = (struct iphdr *)(priv->tx_buf + sizeof(struct ethhdr));
    saddr = &iph->saddr;
    daddr = &iph->daddr;

    netif_info(priv, hw, netdev, "%s(#%d), orig, src:%pI4, dst:%pI4, len:%d\n",
                __func__, __LINE__, saddr, daddr, priv->tx_len);

    in_dev = nic_dev[(netdev == nic_dev[0] ? 1 : 0)]->ip_ptr;
    if (in_dev) {
        if_info = in_dev->ifa_list;
        for (if_info = in_dev->ifa_list; if_info; if_info=if_info->ifa_next) {
#if 0
            printk("label:%s, address=%pI4\n",
               if_info->ifa_label, &if_info->ifa_address);
#endif
            *saddr = *daddr = if_info->ifa_address;
            ((u8 *)saddr)[3]++;
            netif_info(priv, hw, netdev, "%s(#%d), new, src:%pI4, dst:%pI4\n",
                        __func__, __LINE__, saddr, daddr);
            break;
        }
        if (!if_info) {
            /* drop packet */
            netdev->stats.tx_dropped++;
            netif_info(priv, hw, netdev, "%s(#%d), drop packet\n",
                        __func__, __LINE__);
            return;
        }
    }

    iph->check = 0;         /* and rebuild the checksum (ip needs it) */
    iph->check = ip_fast_csum((unsigned char *)iph, iph->ihl);

    netdev->stats.tx_packets++;
    netdev->stats.tx_bytes += priv->tx_len;

    nic_rx(nic_dev[(netdev == nic_dev[0] ? 1 : 0)], priv->tx_len, priv->tx_buf);
}

static netdev_tx_t nic_start_xmit(struct sk_buff *skb,
                                  struct net_device *netdev)
{
    struct nic_priv *priv = netdev_priv(netdev);
    netif_info(priv, drv, netdev, "%s(#%d), orig, src:%pI4, dst:%pI4\n",
                __func__, __LINE__, &(ip_hdr(skb)->saddr), &(ip_hdr(skb)->daddr));
    priv->tx_len = skb->len;
    if (likely(priv->tx_len < MAX_ETH_FRAME_SIZE)) {
        if (priv->tx_len < ETH_ZLEN) {
            memset(priv->tx_buf, 0, ETH_ZLEN);
            priv->tx_len = ETH_ZLEN;
        }
        skb_copy_and_csum_dev(skb, priv->tx_buf);
        dev_kfree_skb_any(skb);
    } else {
        dev_kfree_skb_any(skb);
        netdev->stats.tx_dropped++;
        return NETDEV_TX_OK;
    }

    nic_hw_xmit(netdev);
    return NETDEV_TX_OK;
}

static int nic_validate_addr(struct net_device *netdev)
{
    struct nic_priv *priv = netdev_priv(netdev);
    netif_info(priv, drv, netdev, "%s(#%d), priv:%p\n",
                __func__, __LINE__, priv);
    return eth_validate_addr(netdev);
}

static int nic_change_mtu(struct net_device *netdev, int new_mtu)
{
    struct nic_priv *priv = netdev_priv(netdev);
    netif_info(priv, drv, netdev, "%s(#%d), priv:%p\n",
                __func__, __LINE__, priv);
    return eth_change_mtu(netdev, new_mtu);
}

static int nic_set_mac_addr(struct net_device *netdev, void *addr)
{
    struct nic_priv *priv = netdev_priv(netdev);
    netif_info(priv, drv, netdev, "%s(#%d), priv:%p\n",
                __func__, __LINE__, priv);
    return eth_mac_addr(netdev, addr);
}

/*
 * This function is called to fill up an eth header, since arp is not
 * available on the interface
 */
int snull_header(struct sk_buff *skb, struct net_device *netdev,
                unsigned short type, const void *daddr, const void *saddr,
                unsigned len)
{
    struct nic_priv *priv = netdev_priv(netdev);
    struct ethhdr *eth = (struct ethhdr *)skb_push(skb, ETH_HLEN);
    struct net_device *dst_netdev;

    netif_info(priv, drv, netdev, "%s(#%d)\n",
                __func__, __LINE__);
    dst_netdev = nic_dev[(netdev == nic_dev[0] ? 1 : 0)];
    eth->h_proto = htons(type);
    memcpy(eth->h_source, saddr ? saddr : netdev->dev_addr, netdev->addr_len);
    memcpy(eth->h_dest, dst_netdev->dev_addr, dst_netdev->addr_len);
    return (netdev->hard_header_len);
}

static const struct header_ops snull_header_ops = {
        .create  = snull_header,
};

static const struct net_device_ops nic_netdev_ops = {
    /* Kernel calls ndo_open() and ndo_validate_addr()
     * when you bring up the NIC
     */
    .ndo_open               = nic_open,
    .ndo_validate_addr      = nic_validate_addr,

    /* when you shut down the NIC, kernel call the .ndo_stop() */
    .ndo_stop               = nic_close,

    /* Kernel calls ndo_start_xmit() when it wants to 
     *   transmit a packet. 
     */
    .ndo_start_xmit         = nic_start_xmit,

    /* ndo_change_mtu() is called, when you change MTU */
    .ndo_change_mtu         = nic_change_mtu,

    /* ndo_set_mac_address() is called,
     *   when you change the MAC addr
     */
    .ndo_set_mac_address    = nic_set_mac_addr,
};

static struct net_device* nic_alloc_netdev(void)
{
    struct net_device *netdev;

    netdev = alloc_etherdev(sizeof(struct nic_priv));
    if (!netdev) {
        pr_err("%s(#%d): alloc dev failed",
               __func__, __LINE__);
        return NULL;
    }
    eth_hw_addr_random(netdev);
    netdev->netdev_ops = &nic_netdev_ops;

    /* keep the default flags, just add NOARP */
    netdev->flags |= IFF_NOARP;

    /* There are no explicit users, so this is 
     *     now equivalent to NETIF_F_HW_CSUM. */
    netdev->features |= NETIF_F_HW_CSUM;

    netdev->header_ops = &snull_header_ops;

    return netdev;
}

static int __init brook_init(void)
{
    int ret;
    struct nic_priv *priv;

    nic_dev[0] = nic_alloc_netdev();
    if (!nic_dev[0]) {
        pr_err("%s(#%d): alloc netdev[0] failed", __func__, __LINE__);
        return -ENOMEM;
    }

    nic_dev[1] = nic_alloc_netdev();
    if (!nic_dev[1]) {
        pr_err("%s(#%d): alloc netdev[1] failed", __func__, __LINE__);
        ret = -ENOMEM;
        goto alloc_2nd_failed;
    }

    ret = register_netdev(nic_dev[0]);
    if (ret) {
        pr_err("%s(#%d): reg net driver failed. ret:%d",
               __func__, __LINE__, ret);
        goto reg1_failed;
    }

    ret = register_netdev(nic_dev[1]);
    if (ret) {
        pr_err("%s(#%d): reg net driver failed. ret:%d",
               __func__, __LINE__, ret);
        goto reg2_failed;
    }

    priv = netdev_priv(nic_dev[0]);
    priv->msg_enable = DEF_MSG_ENABLE;
    priv = netdev_priv(nic_dev[1]);
    priv->msg_enable = DEF_MSG_ENABLE;
    return 0;

reg2_failed:
    unregister_netdev(nic_dev[0]);
reg1_failed:
    free_netdev(nic_dev[1]);
alloc_2nd_failed:
    free_netdev(nic_dev[0]);
    return ret;
}
module_init(brook_init);

static void __exit brook_exit(void)
{
    int i;
    pr_info("%s(#%d): remove module", __func__, __LINE__);
    for (i = 0; i < ARRAY_SIZE(nic_dev); i++) {
        unregister_netdev(nic_dev[i]);
        free_netdev(nic_dev[i]);
    }
}
module_exit(brook_exit);

參考資料：

1. Linux Device Drivers, Third Edition, Chapter 17: Network Drivers, https://lwn.net/Kernel/LDD3/,
2. Linux Networking and Network Devices APIs, https://www.kernel.org/doc/htmldocs/networking/index.html

OpenEmbedded - Writing a recipes/package inherit cmake

基本上inherit cmake跟inherit autotools是差不多的，其實cmake class裡面也是有inherit autotool，比較大的差異是，source file在cmake下是放在${PN}目錄下，即package name下，檔案結構如下：

brook@vista:~/oe-core$ tree meta/recipes-support/brook-cmake
meta/recipes-support/brook-cmake
|-- brook-cmake
|   `-- brook-cmake.patch
`-- brook-cmake_1.0.bb
1 directory, 2 files

brook-cmake.patch就是放置CMakeLists.txt、main.c跟LICENSE，其內容如下：

CMakeLists.txt

cmake_minimum_required (VERSION 2.6)
project(brook-cmake-demo)
add_executable(brook-cmake main.c)
install(TARGETS brook-cmake DESTINATION bin)

main.c

#include <stdio.h>

int main(int argc, char *argv[])
{
    printf("hello, cmake\n");
    return 0;
}

brook-cmake_1.0.bb

DESCRIPTION = "Brook CMake Project"
LICENSE = "GPLv2"
LIC_FILES_CHKSUM = "file://LICENSE;md5=5ff2bd2dd80c7cc542a6b8de3ee4ff87"

SRC_URI = "file://brook-cmake.patch \
"

inherit cmake

EXTRA_OEMAKE = "-Wall"

下面這裡是多個版本的寫法

其實寫法都一樣，只是patch file的目錄要包含版本號，檔案結構如下：

brook@vista:~/oe-core/meta/recipes-support$ tree brook-cmake
brook-cmake
|-- brook-cmake-1.0
|   `-- brook-cmake.patch
|-- brook-cmake-2.0
|   `-- brook-cmake.patch
|-- brook-cmake_1.0.bb
`-- brook-cmake_2.0.bb

BB檔與patch的內容跟上面都是一樣的

brook@vista:~/oe-core$ cat meta/recipes-support/brook-cmake/brook-cmake_1.0.bb
DESCRIPTION = "Brook CMake Project"
LICENSE = "GPLv2"
LIC_FILES_CHKSUM = "file://LICENSE;md5=7e4bf6f59b6da8e57ed5425a10a7310b"

SRC_URI = "file://brook-cmake.patch \
"

inherit cmake

BBCLASSEXTEND = "native"

EXTRA_OEMAKE = "-Wall"

brook@vista:~/oe-core$ cat meta/recipes-support/brook-cmake/brook-cmake_2.0.bb
DESCRIPTION = "Brook CMake Project"
LICENSE = "GPLv2"
LIC_FILES_CHKSUM = "file://LICENSE;md5=7e4bf6f59b6da8e57ed5425a10a7310b"

SRC_URI = "file://brook-cmake.patch \
"

inherit cmake

BBCLASSEXTEND = "native"

EXTRA_OEMAKE = "-Wall"

brook@vista:~/oe-core$ cat meta/recipes-support/brook-cmake/brook-cmake-1.0/brook-cmake.patch
From 037c40faba39a11e54f282c3eab5e47a4cf1c7ca Mon Sep 17 00:00:00 2001
From: Brook <rene3210 at gmail.com>
Date: Tue, 27 Sep 2016 20:42:11 +0800
Subject: [PATCH] brook oe demo code

---
 CMakeLists.txt | 5 +++++
 LICENSE        | 1 +
 main.c         | 8 ++++++++
 3 files changed, 14 insertions(+)
 create mode 100644 CMakeLists.txt
 create mode 100644 LICENSE
 create mode 100644 main.c

diff --git a/CMakeLists.txt b/CMakeLists.txt
new file mode 100644
index 0000000..ee4d6d9
--- /dev/null
+++ b/CMakeLists.txt
@@ -0,0 +1,5 @@
+cmake_minimum_required (VERSION 2.6)
+project(brook-cmake-demo)
+add_executable(brook-cmake main.c)
+install(TARGETS brook-cmake DESTINATION bin)
+
diff --git a/LICENSE b/LICENSE
new file mode 100644
index 0000000..0664320
--- /dev/null
+++ b/LICENSE
@@ -0,0 +1 @@
+"GPLv2"
diff --git a/main.c b/main.c
new file mode 100644
index 0000000..d089aad
--- /dev/null
+++ b/main.c
@@ -0,0 +1,8 @@
+#include 
+
+int main(int argc, char *argv[])
+{
+    printf("hello, cmake 1.0\n");
+    return 0;
+}
+
--
2.7.4

brook@vista:~/oe-core$ cat meta/recipes-support/brook-cmake/brook-cmake-2.0/brook-cmake.patch
From 037c40faba39a11e54f282c3eab5e47a4cf1c7ca Mon Sep 17 00:00:00 2001
From: Brook <rene3210 at gmail.com>
Date: Tue, 27 Sep 2016 20:42:11 +0800
Subject: [PATCH] brook oe demo code

---
 CMakeLists.txt | 5 +++++
 LICENSE        | 1 +
 main.c         | 8 ++++++++
 3 files changed, 14 insertions(+)
 create mode 100644 CMakeLists.txt
 create mode 100644 LICENSE
 create mode 100644 main.c

diff --git a/CMakeLists.txt b/CMakeLists.txt
new file mode 100644
index 0000000..ee4d6d9
--- /dev/null
+++ b/CMakeLists.txt
@@ -0,0 +1,5 @@
+cmake_minimum_required (VERSION 2.6)
+project(brook-cmake-demo)
+add_executable(brook-cmake main.c)
+install(TARGETS brook-cmake DESTINATION bin)
+
diff --git a/LICENSE b/LICENSE
new file mode 100644
index 0000000..0664320
--- /dev/null
+++ b/LICENSE
@@ -0,0 +1 @@
+"GPLv2"
diff --git a/main.c b/main.c
new file mode 100644
index 0000000..d089aad
--- /dev/null
+++ b/main.c
@@ -0,0 +1,8 @@
+#include 
+
+int main(int argc, char *argv[])
+{
+    printf("hello, cmake 2.0\n");
+    return 0;
+}
+
--
2.7.4

如果沒有特別指定版本的話，會使用最新的，可以透過設定PREFERRED_VERSION_package_name設定特定版本，如

brook@vista:~/oe-core$ grep -H PREFERRED_VERSION build/conf/local.conf
build/conf/local.conf:PREFERRED_VERSION_brook-cmake = "1.0"

相關資訊可以參考Bitbake User Manual/2.3. Preferences and Providers

參考資料：
1. CMake 入門

BitBake User Manual - CH3.3. Sharing Functionality

BitBake 有metadata sharing的機制，基本上分為兩類，include file(.inc)跟class file(.bbclass)，你可以使用include或require來include .inc檔案，其行為就是會將.inc內容插入include那行的位置中。
include跟require相似，差異是，如果檔案不存在include不會error，但是requre就會，如：

include foo_no_exist.inc
require foo_need_exist.inc

你可以使用iherit來使用class file，使用這指令會去尋找對應的class來使用，如：

inherit autotools

如果每個recipes都需要inherit的話，可以在.conf使用INHERIT指令達成這目的，如：

INHERIT += sanity

example：meta/conf/sanity.conf

# Sanity checks for common user misconfigurations
#
# See sanity.bbclass
#
# Expert users can confirm their sanity with "touch conf/sanity.conf"
BB_MIN_VERSION = "1.27.1"

SANITY_ABIFILE = "${TMPDIR}/abi_version"

SANITY_VERSION ?= "1"
LOCALCONF_VERSION  ?= "1"
LAYER_CONF_VERSION ?= "6"
SITE_CONF_VERSION  ?= "1"

INHERIT += "sanity"

example：meta/classes/sanity.bbclass

參考資料：
1. BitBake User Manual

Linux Kernel（15.2）- platform_device_register()之如何调用driver.probe()

繼Linux Kernel（16.1）- platform_driver_register()之如何调用driver.probe()之後，我們來看如何由platform_device_register调用driver.probe()

int platform_device_register(struct platform_device *pdev)
{
    device_initialize(&pdev->dev);
    arch_setup_pdev_archdata(pdev);
    return platform_device_add(pdev);
}
EXPORT_SYMBOL_GPL(platform_device_register);


int platform_device_add(struct platform_device *pdev)
{
    int i, ret;

    if (!pdev)
        return -EINVAL;

    if (!pdev->dev.parent)
        pdev->dev.parent = &platform_bus;

    pdev->dev.bus = &platform_bus_type;

    switch (pdev->id) {
    default:
        dev_set_name(&pdev->dev, "%s.%d", pdev->name,  pdev->id);
        break;
    case PLATFORM_DEVID_NONE:
        dev_set_name(&pdev->dev, "%s", pdev->name);
        break;
    case PLATFORM_DEVID_AUTO:
        /*
         * Automatically allocated device ID. We mark it as such so
         * that we remember it must be freed, and we append a suffix
         * to avoid namespace collision with explicit IDs.
         */
        ret = ida_simple_get(&platform_devid_ida, 0, 0, GFP_KERNEL);
        if (ret < 0)
            goto err_out;
        pdev->id = ret;
        pdev->id_auto = true;
        dev_set_name(&pdev->dev, "%s.%d.auto", pdev->name, pdev->id);
        break;
    }

    for (i = 0; i < pdev->num_resources; i++) {
        struct resource *p, *r = &pdev->resource[i];

        if (r->name == NULL)
            r->name = dev_name(&pdev->dev);

        p = r->parent;
        if (!p) {
            if (resource_type(r) == IORESOURCE_MEM)
                p = &iomem_resource;
            else if (resource_type(r) == IORESOURCE_IO)
                p = &ioport_resource;
        }

        if (p && insert_resource(p, r)) {
            dev_err(&pdev->dev, "failed to claim resource %d\n", i);
            ret = -EBUSY;
            goto failed;
        }
    }

    pr_debug("Registering platform device '%s'. Parent at %s\n",
         dev_name(&pdev->dev), dev_name(pdev->dev.parent));

    ret = device_add(&pdev->dev);
    if (ret == 0)
        return ret;

 failed:
    if (pdev->id_auto) {
        ida_simple_remove(&platform_devid_ida, pdev->id);
        pdev->id = PLATFORM_DEVID_AUTO;
    }

    while (--i >= 0) {
        struct resource *r = &pdev->resource[i];
        if (r->parent)
            release_resource(r);
    }

 err_out:
    return ret;
}


int device_add(struct device *dev) 
{
    struct device *parent = NULL;
    struct kobject *kobj;
    struct class_interface *class_intf;
    int error = -EINVAL;

    dev = get_device(dev);
    if (!dev)
        goto done;

    if (!dev->p) {
        error = device_private_init(dev);
        if (error)
            goto done;
    }

    /*
     * for statically allocated devices, which should all be converted
     * some day, we need to initialize the name. We prevent reading back
     * the name, and force the use of dev_name()
     */
    if (dev->init_name) {
        dev_set_name(dev, "%s", dev->init_name);
        dev->init_name = NULL;
    }

    /* subsystems can specify simple device enumeration */
    if (!dev_name(dev) && dev->bus && dev->bus->dev_name)
        dev_set_name(dev, "%s%u", dev->bus->dev_name, dev->id);

    if (!dev_name(dev)) {
        error = -EINVAL;
        goto name_error;
    }

    pr_debug("device: '%s': %s\n", dev_name(dev), __func__);

    parent = get_device(dev->parent);
    kobj = get_device_parent(dev, parent);
    if (kobj)
        dev->kobj.parent = kobj;

    /* use parent numa_node */
    if (parent)
        set_dev_node(dev, dev_to_node(parent));

    /* first, register with generic layer. */
    /* we require the name to be set before, and pass NULL */
    error = kobject_add(&dev->kobj, dev->kobj.parent, NULL);
    if (error)
        goto Error;

    /* notify platform of device entry */
    if (platform_notify)
        platform_notify(dev);

    error = device_create_file(dev, &dev_attr_uevent);
    if (error)
        goto attrError;

    error = device_add_class_symlinks(dev);
    if (error)
        goto SymlinkError;
    error = device_add_attrs(dev);
    if (error)
        goto AttrsError;
    error = bus_add_device(dev);
    if (error)
        goto BusError;
    error = dpm_sysfs_add(dev);
    if (error)
        goto DPMError;
    device_pm_add(dev);

    if (MAJOR(dev->devt)) {
        error = device_create_file(dev, &dev_attr_dev);
        if (error)
            goto DevAttrError;

        error = device_create_sys_dev_entry(dev);
        if (error)
            goto SysEntryError;

        devtmpfs_create_node(dev);
    }

    /* Notify clients of device addition.  This call must come
     * after dpm_sysfs_add() and before kobject_uevent().
     */
    if (dev->bus)
        blocking_notifier_call_chain(&dev->bus->p->bus_notifier,
                         BUS_NOTIFY_ADD_DEVICE, dev);

    kobject_uevent(&dev->kobj, KOBJ_ADD);
    bus_probe_device(dev);
    if (parent)
        klist_add_tail(&dev->p->knode_parent,
                   &parent->p->klist_children);

    if (dev->class) {
        mutex_lock(&dev->class->p->mutex);
        /* tie the class to the device */
        klist_add_tail(&dev->knode_class,
                   &dev->class->p->klist_devices);

        /* notify any interfaces that the device is here */
        list_for_each_entry(class_intf,
                    &dev->class->p->interfaces, node)
            if (class_intf->add_dev)
                class_intf->add_dev(dev, class_intf);
        mutex_unlock(&dev->class->p->mutex);
    }
done:
    put_device(dev);
    return error;
 SysEntryError:
    if (MAJOR(dev->devt))
        device_remove_file(dev, &dev_attr_dev);
 DevAttrError:
    device_pm_remove(dev);
    dpm_sysfs_remove(dev);
 DPMError:
    bus_remove_device(dev);
 BusError:
    device_remove_attrs(dev);
 AttrsError:
    device_remove_class_symlinks(dev);
 SymlinkError:
    device_remove_file(dev, &dev_attr_uevent);
 attrError:
    kobject_uevent(&dev->kobj, KOBJ_REMOVE);
    kobject_del(&dev->kobj);
 Error:
    cleanup_device_parent(dev);
    put_device(parent);
name_error:
    kfree(dev->p);
    dev->p = NULL;
    goto done;
}


void bus_probe_device(struct device *dev)
{
    struct bus_type *bus = dev->bus;
    struct subsys_interface *sif;

    if (!bus)
        return;

    if (bus->p->drivers_autoprobe)
        device_initial_probe(dev);

    mutex_lock(&bus->p->mutex);
    list_for_each_entry(sif, &bus->p->interfaces, node)
        if (sif->add_dev)
            sif->add_dev(dev, sif);
    mutex_unlock(&bus->p->mutex);
}


void device_initial_probe(struct device *dev)
{
    __device_attach(dev, true);
}


static int __device_attach(struct device *dev, bool allow_async)
{
    int ret = 0;

    device_lock(dev);
    if (dev->driver) {
        if (klist_node_attached(&dev->p->knode_driver)) {
            ret = 1;
            goto out_unlock;
        }
        ret = device_bind_driver(dev);
        if (ret == 0)
            ret = 1;
        else {
            dev->driver = NULL;
            ret = 0;
        }
    } else {
        struct device_attach_data data = {
            .dev = dev,
            .check_async = allow_async,
            .want_async = false,
        };

        if (dev->parent)
            pm_runtime_get_sync(dev->parent);

        ret = bus_for_each_drv(dev->bus, NULL, &data,
                    __device_attach_driver);
        if (!ret && allow_async && data.have_async) {
            /*
             * If we could not find appropriate driver
             * synchronously and we are allowed to do
             * async probes and there are drivers that
             * want to probe asynchronously, we'll
             * try them.
             */
            dev_dbg(dev, "scheduling asynchronous probe\n");
            get_device(dev);
            async_schedule(__device_attach_async_helper, dev);
        } else {
            pm_request_idle(dev);
        }

        if (dev->parent)
            pm_runtime_put(dev->parent);
    }
out_unlock:
    device_unlock(dev);
    return ret;
}


static int __device_attach_driver(struct device_driver *drv, void *_data)
{
    struct device_attach_data *data = _data;
    struct device *dev = data->dev;
    bool async_allowed;

    /*
     * Check if device has already been claimed. This may
     * happen with driver loading, device discovery/registration,
     * and deferred probe processing happens all at once with
     * multiple threads.
     */
    if (dev->driver)
        return -EBUSY;

    if (!driver_match_device(drv, dev))
        return 0;

    async_allowed = driver_allows_async_probing(drv);

    if (async_allowed)
        data->have_async = true;

    if (data->check_async && async_allowed != data->want_async)
        return 0;

    return driver_probe_device(drv, dev);
}


static inline int driver_match_device(struct device_driver *drv,
                      struct device *dev)
{
    return drv->bus->match ? drv->bus->match(dev, drv) : 1;
}

Linux Kernel（15.1）- platform_driver_register()之如何调用driver.probe()

轉自platform_driver_register()--如何match之后调用probe

int platform_driver_register(struct platform_driver *drv)
{
    drv->driver.bus = &platform_bus_type;/*关联总线*/
    /*关联driver的设备方法*/
    if (drv->probe)
        drv->driver.probe = platform_drv_probe;
    if (drv->remove)
        drv->driver.remove = platform_drv_remove;
    if (drv->shutdown)
        drv->driver.shutdown = platform_drv_shutdown;

    return driver_register(&drv->driver);/*注册驱动*/
}

/******************************************************************************/
struct platform_driver {
    int (*probe)(struct platform_device *);/*匹配到设备后调用，下面分析内核代码怎么调用的*/
    int (*remove)(struct platform_device *);
    void (*shutdown)(struct platform_device *);
    int (*suspend)(struct platform_device *, pm_message_t state);
    int (*resume)(struct platform_device *);
    struct device_driver driver;
    const struct platform_device_id *id_table;
};

struct bus_type platform_bus_type = {
    .name        = "platform",
    .dev_attrs    = platform_dev_attrs,
    .match        = platform_match,
    .uevent        = platform_uevent,
    .pm        = &platform_dev_pm_ops,
};
/********************************************************************************/

int driver_register(struct device_driver *drv)
{
    int ret;
    struct device_driver *other;

    BUG_ON(!drv->bus->p);

    if ((drv->bus->probe && drv->probe) ||
        (drv->bus->remove && drv->remove) ||
        (drv->bus->shutdown && drv->shutdown))
        printk(KERN_WARNING "Driver '%s' needs updating - please use "
            "bus_type methods\n", drv->name);

    other = driver_find(drv->name, drv->bus);
    if (other) {
        put_driver(other);
        printk(KERN_ERR "Error: Driver '%s' is already registered, "
            "aborting...\n", drv->name);
        return -EBUSY;
    }

    ret = bus_add_driver(drv);
    if (ret)
        return ret;
    ret = driver_add_groups(drv, drv->groups);
    if (ret)
        bus_remove_driver(drv);
    return ret;
}

int bus_add_driver(struct device_driver *drv)
{
    struct bus_type *bus;
    struct driver_private *priv;
    int error = 0;

    bus = bus_get(drv->bus);
    if (!bus)
        return -EINVAL;

    pr_debug("bus: '%s': add driver %s\n", bus->name, drv->name);

    priv = kzalloc(sizeof(*priv), GFP_KERNEL);
    if (!priv) {
        error = -ENOMEM;
        goto out_put_bus;
    }
    klist_init(&priv->klist_devices, NULL, NULL);
    priv->driver = drv;
    drv->p = priv;
    priv->kobj.kset = bus->p->drivers_kset;
    error = kobject_init_and_add(&priv->kobj, &driver_ktype, NULL,
                     "%s", drv->name);
    if (error)
        goto out_unregister;

    if (drv->bus->p->drivers_autoprobe) {
        error = driver_attach(drv);
        if (error)
            goto out_unregister;
    }
    klist_add_tail(&priv->knode_bus, &bus->p->klist_drivers);
    module_add_driver(drv->owner, drv);

    error = driver_create_file(drv, &driver_attr_uevent);
    if (error) {
        printk(KERN_ERR "%s: uevent attr (%s) failed\n",
            __func__, drv->name);
    }
    error = driver_add_attrs(bus, drv);
    if (error) {
        /* How the hell do we get out of this pickle? Give up */
        printk(KERN_ERR "%s: driver_add_attrs(%s) failed\n",
            __func__, drv->name);
    }

    if (!drv->suppress_bind_attrs) {
        error = add_bind_files(drv);
        if (error) {
            /* Ditto */
            printk(KERN_ERR "%s: add_bind_files(%s) failed\n",
                __func__, drv->name);
        }
    }

    kobject_uevent(&priv->kobj, KOBJ_ADD);
    return 0;

out_unregister:
    kobject_put(&priv->kobj);
    kfree(drv->p);
    drv->p = NULL;
out_put_bus:
    bus_put(bus);
    return error;
}

int driver_attach(struct device_driver *drv)
{
    /*对总线上的每一个设备都调用__driver_attach*/
    return bus_for_each_dev(drv->bus, NULL, drv, __driver_attach);
}

static int __driver_attach(struct device *dev, void *data)
{
    struct device_driver *drv = data;

    /*
     * Lock device and try to bind to it. We drop the error
     * here and always return 0, because we need to keep trying
     * to bind to devices and some drivers will return an error
     * simply if it didn't support the device.
     *
     * driver_probe_device() will spit a warning if there
     * is an error.
     */

    if (!driver_match_device(drv, dev))
        return 0;

    if (dev->parent)    /* Needed for USB */
        device_lock(dev->parent);
    device_lock(dev);
    if (!dev->driver)
        driver_probe_device(drv, dev);
    device_unlock(dev);
    if (dev->parent)
        device_unlock(dev->parent);

    return 0;
}

static inline int driver_match_device(struct device_driver *drv,
                      struct device *dev)
{
    /*调用总线的match去匹配设备和驱动*/
    return drv->bus->match ? drv->bus->match(dev, drv) : 1;
}

int driver_probe_device(struct device_driver *drv, struct device *dev)
{
    int ret = 0;

    if (!device_is_registered(dev))
        return -ENODEV;

    pr_debug("bus: '%s': %s: matched device %s with driver %s\n",
         drv->bus->name, __func__, dev_name(dev), drv->name);

    pm_runtime_get_noresume(dev);
    pm_runtime_barrier(dev);
    ret = really_probe(dev, drv);
    pm_runtime_put_sync(dev);

    return ret;
}
static int really_probe(struct device *dev, struct device_driver *drv)
{
    int ret = 0;

    atomic_inc(&probe_count);
    pr_debug("bus: '%s': %s: probing driver %s with device %s\n",
         drv->bus->name, __func__, drv->name, dev_name(dev));
    WARN_ON(!list_empty(&dev->devres_head));

    dev->driver = drv;
    if (driver_sysfs_add(dev)) {
        printk(KERN_ERR "%s: driver_sysfs_add(%s) failed\n",
            __func__, dev_name(dev));
        goto probe_failed;
    }
/**********************************************************************************/
    if (dev->bus->probe) {/*首先看总线有没有probe函数，若有则调用，而平台总线没有probe*/
        ret = dev->bus->probe(dev);
        if (ret)
            goto probe_failed;
    } else if (drv->probe) {/*然后看驱动有没有probe函数，若有则调用，*/
        ret = drv->probe(dev);
        if (ret)
            goto probe_failed;
    }
/************************************************************************************/

    driver_bound(dev);
    ret = 1;
    pr_debug("bus: '%s': %s: bound device %s to driver %s\n",
         drv->bus->name, __func__, dev_name(dev), drv->name);
    goto done;

probe_failed:
    devres_release_all(dev);
    driver_sysfs_remove(dev);
    dev->driver = NULL;

    if (ret != -ENODEV && ret != -ENXIO) {
        /* driver matched but the probe failed */
        printk(KERN_WARNING
               "%s: probe of %s failed with error %d\n",
               drv->name, dev_name(dev), ret);
    }
    /*
     * Ignore errors returned by ->probe so that the next driver can try
     * its luck.
     */
    ret = 0;
done:
    atomic_dec(&probe_count);
    wake_up(&probe_waitqueue);
    return ret;
}


/*平台总线的match逻辑*/
static int platform_match(struct device *dev, struct device_driver *drv)
{
    struct platform_device *pdev = to_platform_device(dev);
    struct platform_driver *pdrv = to_platform_driver(drv);

    /* match against the id table first */
    if (pdrv->id_table)
        return platform_match_id(pdrv->id_table, pdev) != NULL;

    /* fall-back to driver name match */
    return (strcmp(pdev->name, drv->name) == 0);/*驱动名字与设备名字要匹配*/
}

Linux Kernel（15）- Platform Devices

很多人心中都有過一個問題What is the difference between Platform driver and normal device driver?，簡單的來說Platform devices就non-discoverable，也就是device本身沒辦法跟系統說"我在這裡"，典型的就是I2C device，它不會通知kernel"我在這裡"，通常是預先知道有個I2C device在那裡，再由software設定好，這類non-discoverable device就適用Platform devices架構來寫。
platform device會被connect在platform bus上，而platform bus是一個虛擬的bus(pseudo-bus)，這樣可以讓整個架構platform driver符合Linux的標準driver model。

這篇會根據The platform device API教導如何寫一個簡單的Platform devices，基本上最基本的platform device只需要name，因為platform bus會根據platform device與platform driver的name是否match執行driver的probe()，而最簡單的platform driver只需要name，跟probe()與remove()即可。

#include <linux/module.h>
#include <linux/platform_device.h>

MODULE_AUTHOR("Brook");
MODULE_DESCRIPTION("Kernel module for demo");
MODULE_LICENSE("GPL");

#define DEVNAME "brook"

#define DYN_ALLOC 1

static struct platform_device brook_device = {
    .name = DEVNAME,
};

static int brook_probe(struct platform_device *pdev)
{
    pr_info("%s(#%d)\n", __func__, __LINE__);
    return 0;
}

static int brook_remove(struct platform_device *pdev)
{
    pr_info("%s(#%d)\n", __func__, __LINE__);
    return 0;
}

static struct platform_driver brook_driver = {
    .driver = {
        .name  = DEVNAME,
        .owner = THIS_MODULE,
    },
    .probe  = brook_probe,
    .remove = brook_remove,
};

static int __init brook_init(void)
{
    int err;
    pr_info("%s(#%d)\n", __func__, __LINE__);

    err = platform_device_register(&brook_device);
    if (err) {
        pr_err("%s(#%d): platform_device_register failed(%d)\n",
                __func__, __LINE__, err);
        return err;
    }

    err = platform_driver_register(&brook_driver);
    if (err) {
        dev_err(&(brook_device.dev), "%s(#%d): platform_driver_register fail(%d)\n",
                __func__, __LINE__, err);
        goto dev_reg_failed;
    }
    return err;

dev_reg_failed:
    platform_device_unregister(&brook_device);

    return err;
}
module_init(brook_init);

static void __exit brook_exit(void)
{
    dev_info(&(brook_device.dev), "%s(#%d)\n", __func__, __LINE__);
    platform_device_unregister(&brook_device);
    platform_driver_unregister(&brook_driver);
}
module_exit(brook_exit);

使用platform_device_register()會導致"brook.0" does not have a release() function, it is broken and must be fixed.的OOPS，可以改用platform_device_alloc() + platform_device_add()，platform_device_alloc()裡面就會做pa->pdev.dev.release = platform_device_release。

#include <linux/module.h>
#include <linux/platform_device.h>

MODULE_AUTHOR("Brook");
MODULE_DESCRIPTION("Kernel module for demo");
MODULE_LICENSE("GPL");

#define DEVNAME "brook"

#define DYN_ALLOC 1

static struct platform_device *brook_device;

static int brook_probe(struct platform_device *pdev)
{
    pr_info("%s(#%d)\n", __func__, __LINE__);
    return 0;
}

static int brook_remove(struct platform_device *pdev)
{
    pr_info("%s(#%d)\n", __func__, __LINE__);
    return 0;
}

static struct platform_driver brook_driver = {
    .driver = {
        .name  = DEVNAME,
        .owner = THIS_MODULE,
    },
    .probe  = brook_probe,
    .remove = brook_remove,
};

static int __init brook_init(void)
{
    int err;
    pr_info("%s(#%d)\n", __func__, __LINE__);

    /* using platform_device_alloc() + platform_device_add() 
     * instead of platform_device_register() to avoid the OOPS, 
     *     "Device 'brook.0' does not have a release() function,
     *      it is broken and must be fixed."
     */
    brook_device = platform_device_alloc(DEVNAME, 0);
    if (!brook_device) {
        pr_err("%s(#%d): platform_device_alloc fail\n",
               __func__, __LINE__);
        return -ENOMEM;
    }

    err = platform_device_add(brook_device);
    if (err) {
        pr_err("%s(#%d): platform_device_add failed\n",
               __func__, __LINE__);
        goto dev_add_failed;
    }

    err = platform_driver_register(&brook_driver);
    if (err) {
        dev_err(&(brook_device->dev), "%s(#%d): platform_driver_register fail(%d)\n",
                __func__, __LINE__, err);
        goto dev_reg_failed;
    }
    return err;

dev_add_failed:
    platform_device_put(brook_device);
dev_reg_failed:
    platform_device_unregister(brook_device);

    return err;
}
module_init(brook_init);

static void __exit brook_exit(void)
{
    dev_info(&(brook_device->dev), "%s(#%d)\n", __func__, __LINE__);
    platform_device_unregister(brook_device);
    platform_driver_unregister(&brook_driver);
}
module_exit(brook_exit);

參考資料：
1. Documentation/driver-model
2. What is the difference between Platform driver and normal device driver?
3. The platform device API
4. Linux Kernel architecture for device drivers
5. platform_driver_register()--如何match之后调用probe
6. Improved dynamically allocated platform_device interface

OpenEmbedded -- Creating and using an SDK

SDK包含了開發時所需的相關檔案，有些還包含了整個開發環境(tool/command)，避免系統的tool/command跟SDK需要的不同造成的error，一個SDK應該包含以下內容：(YOCTO Slides)

1. Compilers or cross-compilers
2. Linkers
3. Library headers
4. Debuggers
5. Custom utilities

這篇文章就是在介紹如何使用Openembedded建立一個generic SDK供他人開發application，使用指令bitbake -v meta-toolchain即可產生generic SDK，並產生一個install的script，放置於oe/oe-core/build/tmp-eglibc/deploy/sdk/底下，執行過程如下

brook@vista:/home/brook/oe/oe-core/build$ bitbake -v meta-toolchain

...

+ chmod +x /home/brook/oe/oe-core/build/tmp-eglibc/deploy/sdk/oecore-x86_64-armv7a-vfp-neon-toolchain-oe-core.0.sh

+ cat /home/brook/oe/oe-core/build/tmp-eglibc/deploy/sdk/oecore-x86_64-armv7a-vfp-neon-toolchain-oe-core.0.tar.bz2

+ rm /home/brook/oe/oe-core/build/tmp-eglibc/deploy/sdk/oecore-x86_64-armv7a-vfp-neon-toolchain-oe-core.0.tar.bz2


NOTE: Tasks Summary: Attempted 1685 tasks of which 1312 didn't need to be rerun and all succeeded.
brook@vista:/home/brook/oe/oe-core/build$ tree tmp-eglibc/deploy/sdk/
tmp-eglibc/deploy/sdk/
`-- oecore-x86_64-armv7a-vfp-neon-toolchain-oe-core.0.sh

0 directories, 1 file

接著直要將底下的script(oecore-x86_64-armv7a-vfp-neon-toolchain-oe-core.0.sh)給developer開發即可，-d後面帶安裝目錄，安裝過程需要SUDO權限，

brook@vista:/home/brook/oe/oe-core/build$ ./tmp-eglibc/deploy/sdk/oecore-x86_64-armv7a-vfp-neon-toolchain-oe-core.0.sh --help
Usage: oecore-x86_64-armv7a-vfp-neon-toolchain-oe-core.0.sh [-y] [-d <dir>]
  -y         Automatic yes to all prompts
  -d <dir>   Install the SDK to <dir>
======== Advanced DEBUGGING ONLY OPTIONS ========
  -S         Save relocation scripts
  -R         Do not relocate executables
  -D         use set -x to see what is going on
brook@vista:~$ /home/brook/oe/oe-core/build/tmp-eglibc/deploy/sdk/oecore-x86_64-armv7a-vfp-neon-toolchain-oe-core.0.sh -d /opt/oe -D
+ printf 'Enter target directory for SDK (default: /usr/local/oecore-x86_64): '
Enter target directory for SDK (default: /usr/local/oecore-x86_64): + '[' /opt/oe = '' ']'
+ echo /opt/oe
/opt/oe

...

+ '[' 0 = 0 ']'
+ /usr/bin/sudo rm /SSD/opt/oe/relocate_sdk.py /SSD/opt/oe/relocate_sdk.sh
+ echo 'SDK has been successfully set up and is ready to be used.'
SDK has been successfully set up and is ready to be used.
+ exit 0

要使用SDK之前，必須先source安裝目錄下開頭為environment-setup-的script，設置相關的環境變數，我的script內容如下

export PATH=/SSD/opt/oe/sysroots/x86_64-oesdk-linux/usr/bin:/SSD/opt/oe/sysroots/x86_64-oesdk-linux/usr/bin/armv
7a-vfp-neon-oe-linux-gnueabi:$PATH
export PKG_CONFIG_SYSROOT_DIR=/SSD/opt/oe/sysroots/armv7a-vfp-neon-oe-linux-gnueabi
export PKG_CONFIG_PATH=/SSD/opt/oe/sysroots/armv7a-vfp-neon-oe-linux-gnueabi/usr/lib/pkgconfig
export CONFIG_SITE=/SSD/opt/oe/site-config-armv7a-vfp-neon-oe-linux-gnueabi
export CC="arm-oe-linux-gnueabi-gcc  -march=armv7-a -mthumb-interwork -mfloat-abi=softfp -mfpu=neon -mthumb-inte
rwork --sysroot=/SSD/opt/oe/sysroots/armv7a-vfp-neon-oe-linux-gnueabi"
export CXX="arm-oe-linux-gnueabi-g++  -march=armv7-a -mthumb-interwork -mfloat-abi=softfp -mfpu=neon -mthumb-int
erwork --sysroot=/SSD/opt/oe/sysroots/armv7a-vfp-neon-oe-linux-gnueabi"
export CPP="arm-oe-linux-gnueabi-gcc -E  -march=armv7-a -mthumb-interwork -mfloat-abi=softfp -mfpu=neon -mthumb-interwork --sysroot=/SSD/opt/oe/sysroots/armv7a-vfp-neon-oe-linux-gnueabi"
export AS="arm-oe-linux-gnueabi-as "
export LD="arm-oe-linux-gnueabi-ld  --sysroot=/SSD/opt/oe/sysroots/armv7a-vfp-neon-oe-linux-gnueabi"
export GDB=arm-oe-linux-gnueabi-gdb
export STRIP=arm-oe-linux-gnueabi-strip
export RANLIB=arm-oe-linux-gnueabi-ranlib
export OBJCOPY=arm-oe-linux-gnueabi-objcopy
export OBJDUMP=arm-oe-linux-gnueabi-objdump
export AR=arm-oe-linux-gnueabi-ar
export NM=arm-oe-linux-gnueabi-nm
export M4=m4
export TARGET_PREFIX=arm-oe-linux-gnueabi-
export CONFIGURE_FLAGS="--target=arm-oe-linux-gnueabi --host=arm-oe-linux-gnueabi --build=x86_64-linux --with-libtool-sysroot=/SSD/opt/oe/sysroots/armv7a-vfp-neon-oe-linux-gnueabi"
export CFLAGS=" -O2 -fexpensive-optimizations -frename-registers -fomit-frame-pointer"
export CXXFLAGS=" -O2 -fexpensive-optimizations -frename-registers -fomit-frame-pointer -fpermissive"
export LDFLAGS="-Wl,-O1 -Wl,--hash-style=gnu -Wl,--as-needed"
export CPPFLAGS=""
export OECORE_NATIVE_SYSROOT="/SSD/opt/oe/sysroots/x86_64-oesdk-linux"
export OECORE_TARGET_SYSROOT="/SSD/opt/oe/sysroots/armv7a-vfp-neon-oe-linux-gnueabi"
export OECORE_ACLOCAL_OPTS="-I /SSD/opt/oe/sysroots/x86_64-oesdk-linux/usr/share/aclocal"
export OECORE_DISTRO_VERSION="20151225"
export OECORE_SDK_VERSION="oe-core.0"
export PYTHONHOME=/SSD/opt/oe/sysroots/x86_64-oesdk-linux/usr
export ARCH=arm
export CROSS_COMPILE=arm-oe-linux-gnueabi-

以下是我用這SDK編譯一個檔案，並放入target中執行

brook@vista:~$ source /opt/oe/environment-setup-armv7a-vfp-neon-oe-linux-gnueabi
brook@vista:~$ cat main.c
#include <stdio.h>

int main(int argc, char *argv[])
{
        printf("hello\n");
        return 0;
}

brook@vista:~$ $CC -o brook-sdk main.c

D:\Projects>adb push z:\brook-sdk /
688 KB/s (5644 bytes in 0.008s)

D:\Projects>adb shell chmod +x /brook-sdk

D:\Projects>adb shell /brook-sdk
hello

開發環境架構圖

參考資料：
1. Yocto Project and OpenEmbedded development course
2. Yocto Project Quick Start -- SDK Generation

OpenEmbedded - Writing Meta Data for adding Kernel Module package

繼OpenEmbedded User Manual - CH3, Writing Meta Data (Adding packages)之後，這一篇是教導如何新增Kernel Module package。 BB檔的寫法與OpenEmbedded User Manual - CH3, Writing Meta Data (Adding packages)雷同，只是我們這次iherit的class是module

/oe-core/meta/recipes-kernel/brook/brook_1.0.bb

inherit module
DESCRIPTION = "Brook Out Tree Kernel Module"
LICENSE = "GPLv2"
LIC_FILES_CHKSUM = "file://LICENSE;md5=5ff2bd2dd80c7cc542a6b8de3ee4ff87"

PR = "r1-${KERNEL_VERSION}"

# This DEPENDS is to serialize kernel module builds
DEPENDS = "virtual/kernel"


SRC_URI = "file://brook.patch \
"

S = "${WORKDIR}/brook-linux-${PV}"

這邊的SRC_URI我是使用patch格式，當然你也可以使用zip格式，但是zip格式需要考慮目錄名稱必須為"${WORKDIR}/brook-linux-${PV}"，即bb檔中的S，但是如果是patch就不用管S目錄名稱為何了。

完整檔案結構如下

後面會陸續介紹每個檔案

    /oe-core/meta/recipes-kernel/brook
    |-- brook_1.0.bb
    |-- files
    |   `-- brook.patch
    `-- git
        |-- LICENSE
        |-- Makefile
        `-- main.c

Makefile

ifneq ($(KERNELRELEASE),)
# obj-m := <module_name>.o
# <module_name>-y := <src1>.o <src2>.o ...

        EXTRA_CFLAGS += -DYAFFS_OUT_OF_TREE

        obj-m := brook.o

        brook-objs := main.o
else
        PWD := $(shell pwd)

modules:
 $(MAKE) -C $(KERNEL_SRC) M=$(PWD) modules

modules_install:
 $(MAKE) -C $(KERNEL_SRC) M=$(PWD) modules_install

clean:
 $(MAKE) -C $(KERNEL_SRC) M=$(PWD) clean
endif

這是一般的Kernel Module寫法，沒有特別的地方，Out Tree build時KERNELRELEASE為空字串，所以會用下面那段。

License的內容就只有"License: GPL"這個字串

main.c

Module的主程式，只是在init與exit時印出簡單字串而已。

#include <linux/module.h>

MODULE_AUTHOR("Brook");
MODULE_DESCRIPTION("Kernel module for demo");
MODULE_LICENSE("GPL");

static int __init brook_init(void)
{
        printk(KERN_INFO "Brook Module Init\n");
        return 0;
}
module_init(brook_init);

static void __exit brook_exit(void)
{
        printk(KERN_INFO "Brook Module Exit\n");
        return;
}
module_exit(brook_exit);

brook.patch

這是我把檔案全部放在git目錄底下，做source control，並用git format-patch產生的，將產生後的檔案放置files/brook.patch。