SPDK/NVMe存储技术分析之SSD设备的发现（二）

接下来重点看看L647对应的函数spck_pci_nvme_enumerate()就好，因为我们的目标是看明白是如何利用Class Code发现SSD设备的。

647         return spdk_pci_nvme_enumerate(pcie_nvme_enum_cb, &enum_ctx);

/* src/spdk-17.07.1/lib/env_dpdk/pci_nvme.c */
 
81 int
82 spdk_pci_nvme_enumerate(spdk_pci_enum_cb enum_cb, void *enum_ctx)
83 {
84      return spdk_pci_enumerate(&g_nvme_pci_drv, enum_cb, enum_ctx);
85 }

注意: L84第一个参数为一个全局变量g_nvme_pci_drv的地址

/* src/spdk-17.07.1/lib/env_dpdk/pci_nvme.c */
 
38 static struct rte_pci_id nvme_pci_driver_id[] = {
39 #if RTE_VERSION >= RTE_VERSION_NUM(16, 7, 0, 1)
40      {
41              .class_id = SPDK_PCI_CLASS_NVME,
42              .vendor_id = PCI_ANY_ID,
43              .device_id = PCI_ANY_ID,
44              .subsystem_vendor_id = PCI_ANY_ID,
45              .subsystem_device_id = PCI_ANY_ID,
46      },
47 #else
48      {RTE_PCI_DEVICE(0x8086, 0x0953)},
49 #endif
50      { .vendor_id = 0, /* sentinel */ },
51 };
..
53 static struct spdk_pci_enum_ctx g_nvme_pci_drv = {
54      .driver = {
55              .drv_flags      = RTE_PCI_DRV_NEED_MAPPING,
56              .id_table       = nvme_pci_driver_id,
..
66      },
67
68      .cb_fn = NULL,
69      .cb_arg = NULL,
70      .mtx = PTHREAD_MUTEX_INITIALIZER,
71      .is_registered = false,
72 };

终于跟Class Code (SPDK_PCI_CLASS_NVME=0x010802)扯上了关系。 全局变量g_nvme_pci_drv就是在L53行定义的，而g_nvme_pci_drv.driver.id_table则是在L38行定义的。

38 static struct rte_pci_id nvme_pci_driver_id[] = {
..
41              .class_id = SPDK_PCI_CLASS_NVME,
..
53 static struct spdk_pci_enum_ctx g_nvme_pci_drv = {
54      .driver = {
..
56              .id_table       = nvme_pci_driver_id,
..

那么，我们只需要进一步深挖spdk_pci_enumerate（）就可以找到SSD设备是如何被发现的了...

/* src/spdk-17.07.1/lib/env_dpdk/pci.c#150 */
 
149 int
150 spdk_pci_enumerate(struct spdk_pci_enum_ctx *ctx,
151                spdk_pci_enum_cb enum_cb,
152                void *enum_ctx)
153 {
...
168
169 #if RTE_VERSION >= RTE_VERSION_NUM(17, 05, 0, 4)
170     if (rte_pci_probe() != 0) {
171 #else
172     if (rte_eal_pci_probe() != 0) {
173 #endif
...
184     return 0;
185 }

省略了一些代码，我们接下来重点关注L170,

170     if (rte_pci_probe() != 0) {
  

从rte_pci_probe()函数的实现开始，我们就深入到DPDK的内部了，代码如下，

/* src/dpdk-17.08/lib/librte_eal/common/eal_common_pci.c#413 */
 
407 /*
408  * Scan the content of the PCI bus, and call the probe() function for
409  * all registered drivers that have a matching entry in its id_table
410  * for discovered devices.
411  */
412 int
413 rte_pci_probe(void)
414 {
415     struct rte_pci_device *dev = NULL;
416     size_t probed = 0, failed = 0;
41