Accessing device information in REMOVE agent
I'd like to be notified when block device goes away (e.g. USB stick unplugged) basically to look if device is in use and possibly initiate clean up. Block hotplug currently is passing only DEVPATH; but it alone is not reliable way to identify it; device may be used under alias names via symbolic links.
Is it safe to access /sys/$DEVPATH in REMOVE agent? Apparently hotplug is called asynchronously i.e. it is possible that /sys entry is already removed?
Would it make sense to add device number? It seems to be natural native "block device ID" :)
TIA
-andrey
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Quoted 4 lines · Andrey Borzenkov
I'd like to be notified when block device goes away (e.g. USB stick unplugged) basically to look if device is in use and possibly initiate clean up. Block hotplug currently is passing only DEVPATH; but it alone is not reliable way to identify it; device may be used under alias names via symbolic links.
What do you mean? DEVPATH is unique for that point in time. There are no alias's in sysfs.
Quoted 2 lines
Is it safe to access
/sys/$DEVPATHin REMOVE agent? Apparently hotplug is called asynchronously i.e. it is possible that /sys entry is already removed?
The /sys entry is probably already removed, but if not, it will disappear any second. So no, it's not safe to try to access it, as it will not work.
Quoted 2 lines
Would it make sense to add device number? It seems to be natural native "block device ID" :)
What "device number"? The major/minor? Why? It's about as unique as DEVPATH is for any point in time.
thanks,
greg k-h
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Quoted 10 lines · Greg KH
Quoted 5 lines · Andrey Borzenkov
I'd like to be notified when block device goes away (e.g. USB stick unplugged) basically to look if device is in use and possibly initiate clean up. Block hotplug currently is passing only DEVPATH; but it alone is not reliable way to identify it; device may be used under alias names via symbolic links.
What do you mean? DEVPATH is unique for that point in time. There are no alias's in sysfs.
Sorry I had to be more precise.
I'd like to (try to) replace current synchronous media change checks in supermount by mounting device on insert and releasing it on remove. For those cases when it makes sense of course, USB sticks in the first place.
But users are free to use any names or links for their device names i.e. they can do
ln -s sda /de/myflash
mount /dev/myflash
and on remove it is rather hard to match this name against DEVPATH. But I can save (major,minor) when mounting and use it to match mounted filesystem on remove.
Quoted 7 lines
Quoted 3 lines
Would it make sense to add device number? It seems to be natural native "block device ID" :)
What "device number"? The major/minor? Why? It's about as unique as DEVPATH is for any point in time.
Hmm ... probably I can just as well use device name (meaning genhd->disk_name) you are right.
Thank you
-andrey
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Quoted 8 lines · Andrey Borzenkov
I'd like to (try to) replace current synchronous media change checks in supermount by mounting device on insert and releasing it on remove. For those cases when it makes sense of course, USB sticks in the first place.
But users are free to use any names or links for their device names i.e. they can do
Quoted 6 lines
ln -s sda /de/myflash
mount/dev/myflashand on remove it is rather hard to match this name against DEVPATH. But I can save (major,minor) when mounting and use it to match mounted filesystem on remove.
You might want to look into what devlabel does, as it sounds like it does much the same thing of what you are wanting to do.
Good luck,
greg k-h
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