[OpenWrt-Devel] block info and DISK_MEDIA_CHANGE events

[Karl Palsson]

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Hi,

I'm trying to get "block mount" to behave well when a microSD
card is removed/inserted from a fixed USB card reader. I've
compiled the uevent-hotplug debugger example from
https://www.kernel.org/doc/pending/hotplug.txt and running that
on my device, I can see that "block info" is somehow triggering
the uevent change notifications I hope. (I can't see anywhere in
the fstools how the uevent is triggered, but it only happens if I
run "block info" manually, "blkid" doesn't trigger any events, so
it's something in block info

Example event (unfortuntely it's identical for card inserted ->
removed and for removed -> inserted)
```
change@/devices/platform/ehci-platform/usb1/1-1/1-1.1/1-1.1:1.0/host0/target0:0:0/0:0:0:0/block/sda
ACTION=change
DEVPATH=/devices/platform/ehci-platform/usb1/1-1/1-1.1/1-1.1:1.0/host0/target0:0:0/0:0:0:0/block/sda
SUBSYSTEM=block DISK_MEDIA_CHANGE=1 MAJOR=8 MINOR=0 DEVNAME=sda
DEVTYPE=disk SEQNUM=637
```

The block hotplug handler sees this notification, but,
unfortunately, it's only looking for add/remove:
http://git.openwrt.org/?p=project/fstools.git;a=blob;f=block.c;h=c6d1b9049145a453205372b93016572b4c332d4a;hb=HEAD#l823

I know of some other platforms that simply script their way out
of this, see:
https://github.com/WRTnode/openwrt-packages/blob/master/linino/uSDaemon/files/etc/init.d/usd
and the uSDaemon:
https://github.com/WRTnode/openwrt-packages/blob/master/linino/uSDaemon/files/sbin/uSDaemon

However, it seems reasonable (to me at least) that "block mount"
should handle these sorts of devices nicely as well as it does
for removable USB sticks. Would it be appropriate to add the
"change" handling, looking _only_ for the DISK_MEDIA_CHANGE
event, and handle mount/umount as appropriate?

Or should something else be converting these into add/remove
events?

Sincerely,
Karl Palsson

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