On Linux, given: a device, for example /dev/sda, and its major and minor numbers, for example 8, 0, how can I know which module / driver is driving it?Can I dig into /sys or /proc to discover that? 
How to find the driver (module) associated with a device on Linux?
linux;drivers;kernel modules
To get this information from sysfs for a device file, first determine the major/minor number by looking at the output of ls -l, eg $ ls -l /dev/sda brw-rw---- 1 root disk 8, 0 Apr 17 12:26 /dev/sdaThe 8, 0 tells us that major number is 8 and the minor is 0. The b at the start of the listing also tells us that it is a block device. Other devices may have a c for character device at the start.If you then look under /sys/dev, you will see there are two directories. One called block and one called char. The no-brainer here is that these are for block and character devices respectively. Each device is then accessible by its major/minor number is this directory. If there is a driver available for the device, it can be found by reading the target of the driver link in this or the device sub-directory. Eg, for my /dev/sda I can simply do:$ readlink /sys/dev/block/8\:0/device/driver../../../../../../../bus/scsi/drivers/sdThis shows that the sd driver is used for the device. If you are unsure if the device is a block or character device, in the shell you could simply replace this part with a *. This works just as well:$ readlink /sys/dev/*/8\:0/device/driver../../../../../../../bus/scsi/drivers/sdBlock devices can also be accessed directly through their name via either /sys/block or /sys/class/block. Eg:$ readlink /sys/block/sda/device/driver../../../../../../../bus/scsi/drivers/sdNote that the existence of various directories in /sys may change depending on the kernel configuration. Also not all devices have a device subfolder. For example, this is the case for partition device files like /dev/sda1. Here you have to access the device for the whole disk (unfortunately there are no sys links for this).A final thing which can be useful to do is to list the drivers for all devices for which they are available. For this you can use globs to select all the directories in which the driver links are present. Eg:$ ls -l /sys/dev/*/*/device/driver ls -l /sys/dev/*/*/driver ls: cannot access ls: No such file or directorylrwxrwxrwx 1 root root 0 Apr 17 12:27 /sys/dev/block/11:0/device/driver -> ../../../../../../../bus/scsi/drivers/srlrwxrwxrwx 1 root root 0 Apr 17 12:26 /sys/dev/block/8:0/device/driver -> ../../../../../../../bus/scsi/drivers/sdlrwxrwxrwx 1 root root 0 Apr 17 12:26 /sys/dev/block/8:16/device/driver -> ../../../../../../../bus/scsi/drivers/sdlrwxrwxrwx 1 root root 0 Apr 17 12:26 /sys/dev/block/8:32/device/driver -> ../../../../../../../../../bus/scsi/drivers/sdlrwxrwxrwx 1 root root 0 Apr 17 20:38 /sys/dev/char/189:0/driver -> ../../../../bus/usb/drivers/usblrwxrwxrwx 1 root root 0 Apr 17 20:38 /sys/dev/char/189:1024/driver -> ../../../../bus/usb/drivers/usblrwxrwxrwx 1 root root 0 Apr 17 20:38 /sys/dev/char/189:128/driver -> ../../../../bus/usb/drivers/usblrwxrwxrwx 1 root root 0 Apr 17 20:38 /sys/dev/char/189:256/driver -> ../../../../bus/usb/drivers/usblrwxrwxrwx 1 root root 0 Apr 17 20:38 /sys/dev/char/189:384/driver -> ../../../../bus/usb/drivers/usblrwxrwxrwx 1 root root 0 Apr 17 12:26 /sys/dev/char/189:512/driver -> ../../../../bus/usb/drivers/usblrwxrwxrwx 1 root root 0 Apr 17 12:26 /sys/dev/char/189:513/driver -> ../../../../../bus/usb/drivers/usblrwxrwxrwx 1 root root 0 Apr 17 12:26 /sys/dev/char/189:514/driver -> ../../../../../bus/usb/drivers/usblrwxrwxrwx 1 root root 0 Apr 17 12:26 /sys/dev/char/189:640/driver -> ../../../../bus/usb/drivers/usblrwxrwxrwx 1 root root 0 Apr 17 12:26 /sys/dev/char/189:643/driver -> ../../../../../bus/usb/drivers/usblrwxrwxrwx 1 root root 0 Apr 17 20:38 /sys/dev/char/189:768/driver -> ../../../../bus/usb/drivers/usblrwxrwxrwx 1 root root 0 Apr 17 20:38 /sys/dev/char/189:896/driver -> ../../../../bus/usb/drivers/usblrwxrwxrwx 1 root root 0 Apr 17 12:26 /sys/dev/char/21:0/device/driver -> ../../../../../../../bus/scsi/drivers/sdlrwxrwxrwx 1 root root 0 Apr 17 12:26 /sys/dev/char/21:1/device/driver -> ../../../../../../../bus/scsi/drivers/sdlrwxrwxrwx 1 root root 0 Apr 17 12:27 /sys/dev/char/21:2/device/driver -> ../../../../../../../bus/scsi/drivers/srlrwxrwxrwx 1 root root 0 Apr 17 12:26 /sys/dev/char/21:3/device/driver -> ../../../../../../../../../bus/scsi/drivers/sdlrwxrwxrwx 1 root root 0 Apr 17 12:26 /sys/dev/char/250:0/device/driver -> ../../../../../../../bus/hid/drivers/hid-genericlrwxrwxrwx 1 root root 0 Apr 17 12:26 /sys/dev/char/250:1/device/driver -> ../../../../../../../bus/hid/drivers/hid-genericlrwxrwxrwx 1 root root 0 Apr 17 12:26 /sys/dev/char/250:2/device/driver -> ../../../../../../../bus/hid/drivers/hid-genericlrwxrwxrwx 1 root root 0 Apr 17 12:26 /sys/dev/char/252:0/device/driver -> ../../../../../../../bus/scsi/drivers/sdlrwxrwxrwx 1 root root 0 Apr 17 12:26 /sys/dev/char/252:1/device/driver -> ../../../../../../../bus/scsi/drivers/sdlrwxrwxrwx 1 root root 0 Apr 17 12:27 /sys/dev/char/252:2/device/driver -> ../../../../../../../bus/scsi/drivers/srlrwxrwxrwx 1 root root 0 Apr 17 12:26 /sys/dev/char/252:3/device/driver -> ../../../../../../../../../bus/scsi/drivers/sdlrwxrwxrwx 1 root root 0 Apr 17 19:53 /sys/dev/char/254:0/device/driver -> ../../../bus/pnp/drivers/rtc_cmoslrwxrwxrwx 1 root root 0 Apr 17 19:53 /sys/dev/char/29:0/device/driver -> ../../../bus/platform/drivers/simple-framebufferlrwxrwxrwx 1 root root 0 Apr 17 19:53 /sys/dev/char/4:64/device/driver -> ../../../bus/pnp/drivers/seriallrwxrwxrwx 1 root root 0 Apr 17 19:53 /sys/dev/char/4:65/device/driver -> ../../../bus/platform/drivers/serial8250lrwxrwxrwx 1 root root 0 Apr 17 19:53 /sys/dev/char/4:66/device/driver -> ../../../bus/platform/drivers/serial8250lrwxrwxrwx 1 root root 0 Apr 17 19:53 /sys/dev/char/4:67/device/driver -> ../../../bus/platform/drivers/serial8250lrwxrwxrwx 1 root root 0 Apr 17 12:26 /sys/dev/char/6:0/device/driver -> ../../../bus/pnp/drivers/parport_pclrwxrwxrwx 1 root root 0 Apr 17 12:26 /sys/dev/char/99:0/device/driver -> ../../../bus/pnp/drivers/parport_pcFinally, to diverge from the question a bit, I will add another /sys glob trick to get a much broader perspective on which drivers are being used by which devices (though not necessarily those with a device file):find /sys/bus/*/drivers/* -maxdepth 1 -lname '*devices*' -lsUpdateLooking more closely at the output of udevadm, it appears to work by finding the canonical /sys directory (as you would get if you dereferenced the major/minor directories above), then working its way up the directory tree, printing out any information that it finds. This way you get information about parent devices and any drivers they use as well.To experiment with this I wrote the script below to walk up the directory tree and display information at each relevant level. udev seems to look for readable files at each level, with their names and contents being incorporated in ATTRS. Instead of doing this I display the contents of the uevent files at each level (seemingly the presence of this defines a distinct level rather than just a subdirectory). I also show the basename of any subsystem links I find and this showing how the device fits in this hierarchy. udevadm does not display the same information, so this is a nice complementary tool. The parent device information (eg PCI information) is also useful if you want to match the output of other tools like lshw to higher level devices.#!/bin/bashdev=$(readlink -m $1)# test for block/character deviceif [ -b $dev ]; then  mode=blockelif [ -c $dev ]; then  mode=charelse  echo $dev is not a device file >&2  exit 1fi# stat outputs major/minor in hex, convert to decimaldata=( $(stat -c '%t %T' $dev) ) || exit 2major=$(( 0x${data[0]} ))minor=$(( 0x${data[1]} ))echo -e Given device:     $1echo -e Canonical device: $devecho -e Major: $majorecho -e Minor: $minor\n# sometimes nodes have been created for devices that are not presentdir=$(readlink -f /sys/dev/$mode/$major\:$minor)if ! [ -e $dir ]; then  echo No /sys entry for $dev >&2  exit 3fi# walk up the /sys hierarchy one directory at a time# stop when there are three levels left while [[ $dir == /*/*/* ]]; do  # it seems the directory is only of interest if there is a 'uevent' file  if [ -e $dir/uevent ]; then    echo $dir:    echo   Uevent:    sed 's/^/    /' $dir/uevent    # check for subsystem link    if [ -d $dir/subsystem ]; then        subsystem=$(readlink -f $dir/subsystem)        echo -e \n  Subsystem:\n    ${subsystem##*/}    fi    echo  fi  # strip a subdirectory  dir=${dir%/*}done