如何将 /proc/bus/usb/devices 条目映射到 /dev/sdX 设备？

Question

I need to know how I can figure out to which entry in /proc/bus/usb/devices a /dev/sdX device maps to. Basically, I need to know the vendor id and product id of a given USB stick (which may not have a serial number).

In my case, I have this entry for my flash drive in /proc/bus/usb/devices:

T:  Bus=01 Lev=01 Prnt=01 Port=00 Cnt=01 Dev#=  6 Spd=480 MxCh= 0
D:  Ver= 2.00 Cls=00(>ifc ) Sub=00 Prot=00 MxPS=64 #Cfgs=  1
P:  Vendor=0781 ProdID=5530 Rev= 2.00
S:  Manufacturer=SanDisk
S:  Product=Cruzer
S:  SerialNumber=0765400A1BD05BEE
C:* #Ifs= 1 Cfg#= 1 Atr=80 MxPwr=200mA
I:* If#= 0 Alt= 0 #EPs= 2 Cls=08(stor.) Sub=06 Prot=50 Driver=usb-storage
E:  Ad=81(I) Atr=02(Bulk) MxPS= 512 Ivl=0ms
E:  Ad=02(O) Atr=02(Bulk) MxPS= 512 Ivl=0ms

I happen to know that in my case it is /dev/sda, but I'm not sure how I can figure this out in code. My first approach was to loop through all /dev/sdXX devices and issue a SCSI_IOCTL_GET_BUS_NUMBER and/or SCSI_IOCTL_GET_IDLUN request, but the information returned doesn't help me match it up:

/tmp # ./getscsiinfo /dev/sda
SCSI bus number: 8
ID: 00
LUN: 00
Channel: 00
Host#: 08
four_in_one: 08000000
host_unique_id: 0

I'm not sure how I can use the SCSI bus number or the ID, LUN, Channel, Host to map it to the entry in /proc/bus/usb/devices. Or how I could get the SCSI bus number from the /proc/bus/usb/001/006 device, which is a usbfs device and doesn't appear to like the same ioctl's:

/tmp # ./getscsiinfo /proc/bus/usb/001/006
Could not get bus number: Inappropriate ioctl for device

Here's the test code for my little getscsiinfo test tool:

#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <errno.h>
#include <scsi/scsi.h>
#include <scsi/sg.h>
#include <sys/ioctl.h>

struct scsi_idlun
{
    int four_in_one;
    int host_unique_id;
};

int main(int argc, char** argv) {
    if (argc != 2)
        return 1;

    int fd = open(argv[1], O_RDONLY | O_NONBLOCK);
    if (fd < 0)
    {
        printf("Error opening device: %m\n");
        return 1;
    }

    int busNumber = -1;
    if (ioctl(fd, SCSI_IOCTL_GET_BUS_NUMBER, &busNumber) < 0)
    {
        printf("Could not get bus number: %m\n");
        close(fd);
        return 1;
    }

    printf("SCSI bus number: %d\n", busNumber);

    struct scsi_idlun argid;
    if (ioctl(fd, SCSI_IOCTL_GET_IDLUN, &argid) < 0)
    {
        printf("Could not get id: %m\n");
        close(fd);
        return 1;
    }

    printf("ID: %02x\n", argid.four_in_one & 0xFF);
    printf("LUN: %02x\n", (argid.four_in_one >> 8) & 0xFF);
    printf("Channel: %02x\n", (argid.four_in_one >> 16) & 0xFF);
    printf("Host#: %02x\n", (argid.four_in_one >> 24) & 0xFF);
    printf("four_in_one: %08x\n", (unsigned int)argid.four_in_one);
    printf("host_unique_id: %d\n", argid.host_unique_id);

    close(fd);
    return 0;
}

Does anyone have any idea?

Answer 1

I believe you can collect such information using libudev library.

Here are some details about it: http://www.signal11.us/oss/udev/

I found something like this on above site:

.. Using libudev, we'll be able to inspect the devices, including their Vendor ID (VID), Product ID (PID), serial number, and device strings, without ever opening the device. Further, libudev will tell us exactly where inside /dev the device's node is located, giving the application a robust and distribution-independent way of accessing the device. ...

Answer 2

udevadm is capable of what your are trying to achieve.

udevadm info -a -p $(udevadm info -q path -n /dev/sda)

udevadm 's sources will tell you how it is done.

Answer 3

This isn't all that easy, nor very well documented (at least from a high-level perspective). The following should work in Kernel's from version 3.1 upward (at least).

I have found the easiest (probably not the only way) is to navigate from the block device entry and test each block device until you find the one that matches your USB entry.

For example, given a block device in /sys/block , such as sdb , you can find the hardware device descriptor entry like this:

# cd /sys/block
# cd $(readlink sdb); cd ../../../../../..
# ls -l
total 0
drwxr-xr-x 6 root root     0 Aug 14 10:47 1-1:1.0
-rw-r--r-- 1 root root  4096 Aug 14 10:52 authorized
-rw-r--r-- 1 root root  4096 Aug 14 10:52 avoid_reset_quirk
-r--r--r-- 1 root root  4096 Aug 14 10:47 bcdDevice
-rw-r--r-- 1 root root  4096 Aug 14 10:49 bConfigurationValue
-r--r--r-- 1 root root  4096 Aug 14 10:47 bDeviceClass
-r--r--r-- 1 root root  4096 Aug 14 10:49 bDeviceProtocol
-r--r--r-- 1 root root  4096 Aug 14 10:49 bDeviceSubClass
-r--r--r-- 1 root root  4096 Aug 14 10:49 bmAttributes
-r--r--r-- 1 root root  4096 Aug 14 10:49 bMaxPacketSize0
-r--r--r-- 1 root root  4096 Aug 14 10:49 bMaxPower
-r--r--r-- 1 root root  4096 Aug 14 10:49 bNumConfigurations
-r--r--r-- 1 root root  4096 Aug 14 10:49 bNumInterfaces
-r--r--r-- 1 root root  4096 Aug 14 10:49 busnum
-r--r--r-- 1 root root  4096 Aug 14 10:52 configuration
-r--r--r-- 1 root root 65553 Aug 14 10:47 descriptors
-r--r--r-- 1 root root  4096 Aug 14 10:52 dev
-r--r--r-- 1 root root  4096 Aug 14 10:49 devnum
-r--r--r-- 1 root root  4096 Aug 14 10:52 devpath
lrwxrwxrwx 1 root root     0 Aug 14 10:47 driver -> ../../../../../../bus/usb/drivers/usb
drwxr-xr-x 3 root root     0 Aug 14 10:52 ep_00
-r--r--r-- 1 root root  4096 Aug 14 10:47 idProduct
-r--r--r-- 1 root root  4096 Aug 14 10:47 idVendor
-r--r--r-- 1 root root  4096 Aug 14 10:52 ltm_capable
-r--r--r-- 1 root root  4096 Aug 14 10:47 manufacturer
-r--r--r-- 1 root root  4096 Aug 14 10:49 maxchild
lrwxrwxrwx 1 root root     0 Aug 14 10:52 port -> ../1-0:1.0/port1
drwxr-xr-x 2 root root     0 Aug 14 10:52 power
-r--r--r-- 1 root root  4096 Aug 14 10:47 product
-r--r--r-- 1 root root  4096 Aug 14 10:52 quirks
-r--r--r-- 1 root root  4096 Aug 14 10:47 removable
--w------- 1 root root  4096 Aug 14 10:52 remove
-r--r--r-- 1 root root  4096 Aug 14 10:47 serial
-r--r--r-- 1 root root  4096 Aug 14 10:49 speed
lrwxrwxrwx 1 root root     0 Aug 14 10:47 subsystem -> ../../../../../../bus/usb
-rw-r--r-- 1 root root  4096 Aug 14 10:47 uevent
-r--r--r-- 1 root root  4096 Aug 14 10:52 urbnum
-r--r--r-- 1 root root  4096 Aug 14 10:49 version

(You can find excellent documentation for the contents of the USB Descriptor here on the BeyondLogic site. )

Given the above, you should be able to map one or more of the USB device fields to the contents of /proc/bus/usb/devices . I find that the serial number is the easiest to match on, so that if you were to cat serial above, you would get the same serial number as listed:

T:  Bus=01 Lev=01 Prnt=01 Port=00 Cnt=01 Dev#=  2 Spd=480 MxCh= 0
D:  Ver= 2.00 Cls=00(>ifc ) Sub=00 Prot=00 MxPS=64 #Cfgs=  1
P:  Vendor=0781 ProdID=5575 Rev=01.26
S:  Manufacturer=SanDisk
S:  Product=Cruzer Glide
S:  SerialNumber=4C530100801115115112
C:  #Ifs= 1 Cfg#= 1 Atr=80 MxPwr=200mA
I:  If#= 0 Alt= 0 #EPs= 2 Cls=08(stor.) Sub=06 Prot=50 Driver=usb-storage

If you go to /sys/block , you can list the full path to the host device entry in the storage driver sysfs entry for each device. Typically, I do this using some programmatic means instead of at the shell prompt, but here you can see the links themselves:

# ls -l sd*
lrwxrwxrwx 1 root root 0 Aug 14 10:45 sda -> ../devices/pci0000:00/0000:00:10.0/host32/target32:0:0/32:0:0:0/block/sda
lrwxrwxrwx 1 root root 0 Aug 14 10:47 sdb -> ../devices/pci0000:00/0000:00:11.0/0000:02:03.0/usb1/1-1/1-1:1.0/host33/target33:0:0/33:0:0:0/block/sdb

Note that you mustn't make any assumptions about the numbers you see in the links. Depending upon the bus subsystem, the mappings could be quite different. For example, on a Raspberry Pi, it looks like this:

# ls -l sd*
lrwxrwxrwx 1 root root 0 Aug 13 23:54 sda -> ../devices/platform/soc/3f980000.usb/usb1/1-1/1-1.4/1-1.4:1.0/host3/target3:0:0/3:0:0:0/block/sda
lrwxrwxrwx 1 root root 0 Aug 13 23:54 sdb -> ../devices/platform/soc/3f980000.usb/usb1/1-1/1-1.3/1-1.3:1.0/host4/target4:0:0/4:0:0:0/block/sdb

So, the best approach is to take the approach listed at the top and navigate relative to the storage driver to find the USB device descriptor.

I'd be curious about more authoritative answers to this. The method above was arrived at by trial-and-error but has been working on several different devices and Kernels with no problem.

Answer 4

For anyone using a system without udev, this link has the exact answer you're looking for:

http://www.spinics.net/lists/linux-usb/msg60916.html

Answer 5

Instead of using proc/bus/usb which is for usbfs you can use /proc/scsi/scsi. In there you can find the Vendor and Serial number with specific channel ID and LUN number.