Hi,
Le 2012-06-28 13:11, Kay Sievers a écrit :
On Thu, Jun 28, 2012 at 12:39 PM, <quidame@xxxxxxxxxxx> wrote:
Since kernel 2.6.37, some infos are available in /sys for associated
loop
devices, especially the backing file. Is it poosible to introduce
the
BACKING_FILE variable for associated loop devices ?
Why would you *ever* want to mirror easily in /sys accessible kernel
variables?
Because it reflects the status of a block device. If I run
# losetup /dev/loop0 /dev/sda1
# udevadm info --attribute-walk --name loop0
[...]
ATTR{removable}=="0"
ATTR{ro}=="0"
ATTR{size}=="4096512"
[...]
Nothing about the backing file, except we know the loop device is
associated because its size is not "0". Its a poor and unusable
information. And yes, the backing file name is easily accessible in
/sys; but it is also the case for "removable", "ro" and "size". (OK,
this is not about "ENV{BACKING_FILE}", but "ATTR{backing_file}". The
first one was a suggestion, the second one is another.)
That is usually the wrong thing to do, because it can get
out-of-sync,
and udev would pretend something that is not true anymore.
Not sure:
# losetup -d /dev/loop0
# losetup /dev/loop0 /dev/sdc1 # sdc is USB stick
# udevadm info --export --query property --name loop0
BACKING_FILE='/dev/sdc1'
DEVLINKS='/dev/disk/by-label/mini /dev/disk/by-uuid/7B55-DC7E'
DEVNAME='/dev/loop0'
DEVPATH='/devices/virtual/block/loop0'
DEVTYPE='disk'
ID_FS_LABEL='mini'
ID_FS_LABEL_ENC='mini'
ID_FS_TYPE='vfat'
ID_FS_USAGE='filesystem'
ID_FS_UUID='7B55-DC7E'
ID_FS_UUID_ENC='7B55-DC7E'
ID_FS_VERSION='FAT32'
MAJOR='7'
MINOR='0'
SUBSYSTEM='block'
UDEV_LOG='3'
UDISKS_PRESENTATION_NOPOLICY='1'
USEC_INITIALIZED='96227881'
I wildly remove the usb stick, and the same command leads to the same
results. This means BACKING_FILE, DEVLINKS and ID_FS_* variables are
'out-of-sync'.
But:
# udevadm trigger --sysname-match=loop0
# udevadm info --export --query=property --name=loop0
BACKING_FILE='/dev/sdc1 _deleted_'
DEVNAME='/dev/loop0'
DEVPATH='/devices/virtual/block/loop0'
DEVTYPE='disk'
MAJOR='7'
MINOR='0'
SUBSYSTEM='block'
UDEV_LOG='3'
UDISKS_PRESENTATION_NOPOLICY='1'
USEC_INITIALIZED='96227881'
And:
# losetup /dev/loop0
/dev/loop0: [0005]:39712 (/dev/sdc1)
Here you can see that the only one relevant information is
BACKING_FILE='/dev/sdc1 _deleted_'
But, really I don't care: if 'udevadm info --attribute-walk --name
loop0' can provide something as
[...]
ATTR{removable}=="0"
ATTR{ro}=="0"
ATTR{size}=="7813120"
ATTR{backing_file}=="/dev/sdc1 (deleted)"
[...]
it' s the same for me. What do you think about that ?
Cheers,
quidame
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