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linux中/dev/bsg的作用是什么

2026-08-18 23:11:37

下面把你上面那段关于

"/dev/bsg" 的说明逐句拆成「中文原句 → English translation」，术语按 Linux 内核 / SCSI / 存储运维口径对齐：BSG = Block SCSI Generic；SG_IO 保留大写；CDB = Command Descriptor Block；H:C:T:L = Host:Channel:Target:LUN；Enclosure = 磁盘柜 / 背板（SES 管理对象）；PR = Persistent Reservation；RPMB = Replay Protected Memory Block。

它不是“存数据的磁盘”

""/dev/bsg/""（BSG = Block SCSI Generic，块层 SCSI 通用透传接口）不是给你存数据的磁盘，也不是

""/dev/sda1"" 那种“可读写的块设备文件”；它是 Linux 给存储/SCSI 类硬件留的一个底层命令通道，供用户态工具直接向设备发 SCSI/CDB 命令。

"/dev/bsg/" (BSG = Block SCSI Generic, i.e. the block-layer SCSI generic pass-through interface) is not a disk for storing data, nor is it a read/write block-special file like

"/dev/sda1"; it is a low-level command channel that Linux exposes for storage/SCSI-class hardware, allowing user-space tools to send SCSI CDB (Command Descriptor Block) commands directly to a device.

它到底是什么

从 Linux 2.6.24 起，内核增加了一套替代/补充传统

""/dev/sgN"" 的 BSG 驱动。

Starting from Linux 2.6.24, the kernel introduced the BSG (block SCSI generic) driver as a replacement for, or supplement to, the traditional

"/dev/sgN" (SCSI generic) interface .

它会为每个被 SCSI 中间层识别到的设备（SAS、SATA、NVMe 走 SCSI 封装、UFS、RAID 卡、Enclosure 等）在

""/dev/bsg/"" 下创建一个字符设备节点，名字一般是：

For each device recognized by the SCSI mid-layer — such as SAS disks, SATA disks, NVMe devices behind a SCSI translation layer, UFS devices, RAID controllers, and SES enclosures — the BSG driver creates a character device node under

"/dev/bsg/", conventionally named:

/dev/bsg/H:C:T:L

其中 H=Host（适配器）、C=Channel/Controller、T=Target、L=LUN（逻辑单元号）。

where H = Host (SCSI host / HBA adapter), C = Channel / Controller, T = Target, and L = LUN (Logical Unit Number) .

内核源码里也能印证：BSG 是把一个

"request_queue" 注册成字符设备，对外提供

"SG_IO"、SCSI 信息查询、超时设置等 ioctl，让应用程序绕过

"sd"（磁盘）、

"sr"（光驱）这些“上层驱动抽象”，直接碰到底层队列去送命令。

This is also consistent with the kernel implementation: BSG registers a

"request_queue" as a character device, and exposes ioctls such as

"SG_IO", SCSI inquiry / VPD retrieval, and timeout configuration, so that an application can bypass the upper-level abstractions of

"sd" (SCSI disk) and

"sr" (SCSI CD-ROM) and submit commands straight down to the underlying block / SCSI queue .

谁在用、用来干什么

典型场景都不是“普通读写文件”，而是存储运维/排障/厂商工具：

The typical use cases are not ordinary file I/O, but storage operations, troubleshooting, and vendor-specific utilities:

- 查硬盘/SSD 的 VPD 页、Serial、Firmware、Supported Log PagesQuerying a HDD/SSD’s VPD pages, serial number, firmware revision, and supported log pages.

- 发 SMART、Read Log、Write Log、Mode Select/Page 改设备参数Issuing SMART commands, LOG SENSE / LOG SELECT, and MODE SELECT / MODE PAGE operations to modify device parameters.

- SAS expander / 背板 / 磁盘柜（Enclosure）管理、LED 定位灯Managing SAS expanders, backplanes, and SES enclosures, including activating the locate / fault LED on a drive slot.

- 多路径 / 集群里的 SCSI Persistent Reservation（PR）：

"reserve" /

"release" /

"preempt"Handling SCSI Persistent Reservations (PR) in multipath or clustered environments:

"RESERVE",

"RELEASE",

"PREEMPT".

- UFS 设备的 RPMB 安全分区访问（很多工具就直接用

""/dev/bsg/0:0:0:49476""）Accessing the RPMB (Replay Protected Memory Block) secure partition of a UFS device — many tools talk to it directly through a node such as

"/dev/bsg/0:0:0:49476" via SECURITY PROTOCOL IN/OUT .

- 光驱刻录、磁带机、扫描仪等“没有块设备抽象”的 SCSI 外设Driving SCSI peripherals that have no block-device abstraction at all, such as CD/DVD burners, tape drives, and scanners .

像

"sg3_utils"、

"sdparm"、

"lsscsi -g"、

"smartctl"（部分后端）、

"ufs-utils" 这类工具都能同时吃

""/dev/sgN"" 和

""/dev/bsg/H:C:T:L"" 。

英文翻译

Tools such as

"sg3_utils",

"sdparm",

"lsscsi -g",

"smartctl" (for some backends), and

"ufs-utils" can operate against either

"/dev/sgN" or

"/dev/bsg/H:C:T:L" .

中文

和

""/dev/sgN"" 的区别（一句话版）

""/dev/sgN""：老牌 SCSI 上层通用驱动，字符设备，覆盖广。

英文翻译

"/dev/sgN": the long-standing SCSI generic (sg) upper-layer driver; a character device with broad coverage across SCSI devices .

""/dev/bsg/...""：走块层请求队列的新一代透传，支持 sg v4 接口、SCSI 双向命令、MQ 队列，更贴近现代存储栈。

"/dev/bsg/...": a newer pass-through path that rides on the block-layer request queue, supporting the sg v4 interface, bidirectional SCSI commands, and blk-mq queues — closer to the modern storage I/O stack .

运维注意点

这些节点通常权限是

"crw------- root:root" 或归

"disk" 组，别给普通用户放开。

These nodes are normally created with permissions such as

"crw------- root:root", or owned by the

"disk" group; do not grant ordinary users access to them.

对它做

"SG_IO" 不是“读个文件”那么无害——一个错误的 MODE SELECT / FORMAT UNIT / PR PREEMPT 可能直接改配置、踢掉集群锁、甚至清盘。

Issuing

"SG_IO" against them is far from as harmless as “reading a file”: a wrong MODE SELECT, FORMAT UNIT, or PR PREEMPT can reconfigure the device, evict a cluster reservation, or even wipe the media.

在容器/快照/只读系统里看到

""/dev/bsg"" 是正常的（尤其 Ubuntu Snap 的 core 镜像、服务器 dmesg 里），只要没人在上面跑底层工具，就当它“存在但不活跃”。

Seeing

"/dev/bsg" inside containers, snapshots, or read-only systems is normal — e.g. in Ubuntu Snap

"core" images or server

"dmesg" output; as long as nothing is running low-level tools against those nodes, treat them as “present but idle”.

如果你愿意，我可以把这段再压成一版「BSG / sg / nvme-cli / ufs-utils 命令通道对照表」，方便你贴在实验报告或运维 Wiki 里。

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