fix for nvme device path (#4866)

Summary:
nvme device path doesn't have "block" as like "nvme/nvme0/nvme0n1"
or "nvme/nvme0/nvme0n1/nvme0n1p1". the last directory such as
"nvme0n1p1" should be removed if nvme drive is partitioned.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/4866

Differential Revision: D13627824

Pulled By: riversand963

fbshipit-source-id: 09ab968f349f3dbb890beea20193f1359b17d317

env/io_posix.cc

@@ -83,10 +83,14 @@ size_t GetLogicalBufferSize(int __attribute__((__unused__)) fd) {
   if (!device_dir.empty() && device_dir.back() == '/') {
     device_dir.pop_back();
   }
-  // NOTE: sda3 does not have a `queue/` subdir, only the parent sda has it.
+  // NOTE: sda3 and nvme0n1p1 do not have a `queue/` subdir, only the parent sda
+  // and nvme0n1 have it.
   // $ ls -al '/sys/dev/block/8:3'
   // lrwxrwxrwx. 1 root root 0 Jun 26 01:38 /sys/dev/block/8:3 ->
   // ../../block/sda/sda3
+  // $ ls -al '/sys/dev/block/259:4'
+  // lrwxrwxrwx 1 root root 0 Jan 31 16:04 /sys/dev/block/259:4 ->
+  // ../../devices/pci0000:17/0000:17:00.0/0000:18:00.0/nvme/nvme0/nvme0n1/nvme0n1p1
   size_t parent_end = device_dir.rfind('/', device_dir.length() - 1);
   if (parent_end == std::string::npos) {
     return kDefaultPageSize;
@@ -95,8 +99,11 @@ size_t GetLogicalBufferSize(int __attribute__((__unused__)) fd) {
   if (parent_begin == std::string::npos) {
     return kDefaultPageSize;
   }
-  if (device_dir.substr(parent_begin + 1, parent_end - parent_begin - 1) !=
+  std::string parent =
-      "block") {
+      device_dir.substr(parent_begin + 1, parent_end - parent_begin - 1);
+  std::string child = device_dir.substr(parent_end + 1, std::string::npos);
+  if (parent != "block" &&
+      (child.compare(0, 4, "nvme") || child.find('p') != std::string::npos)) {
     device_dir = device_dir.substr(0, parent_end);
   }
   std::string fname = device_dir + "/queue/logical_block_size";