On 03/09/2016 09:29 AM, Martin Pitt wrote: > Martin Pitt [2016-03-09 8:52 +0100]: >>> I get (w/ qemu-system 1:2.5+dfsg-4~bpo8+1) with current git master >>> (no changes): >>> mount: /dev/vdb1 is write-protected, mounting read-only >>> >>> So I can't really reproduce it. :-( >> >> I now get the same. I must have wrecked something on Monday, I figure. > > I'm not hallucinating after all. I just tried this again: > > ./run-from-checkout tests/testpkg-simple/ --shell --- qemu > adt-xenial-amd64-cloud.img > > Then ssh'ed in, and ran > > sudo apt-get install -y kpartx > sudo kpartx -av /dev/baseimage > sudo mount /dev/mapper/baseimage1 /mnt > (no "readonly" warning here) > sudo touch /mnt/foo > (succeeded!) > ls -l /mnt/foo > -rw-r--r-- 1 root root 0 Mar 9 08:22 /mnt/foo
Well, this appears to be a bug in kpartx that it does not recognize
that /dev/baseimage is write-protected and thus the dm device is not
marked as write-protected.
If I don't ssh in but connect via minicom, I also see kernel logs,
and I get:
root@autopkgtest:~# mount /dev/mapper/baseimage1 /mnt
[ 76.106053] blk_update_request: I/O error, dev vdb, sector 2048
[ 76.108045] blk_update_request: I/O error, dev vdb, sector 2048
[ 76.109563] Buffer I/O error on dev dm-0, logical block 0, lost sync page
write
root@autopkgtest:~# [ 77.609597] blk_update_request: I/O error, dev vdb,
sector 4728283
[ 77.612648] blk_update_request: I/O error, dev vdb, sector 4728538
[ 77.614416] blk_update_request: I/O error, dev vdb, sector 4728793
[ 77.616187] blk_update_request: I/O error, dev vdb, sector 4720864
[ 77.617945] blk_update_request: I/O error, dev vdb, sector 4721119
[ 77.619711] blk_update_request: I/O error, dev vdb, sector 4721374
[ 77.621469] blk_update_request: I/O error, dev vdb, sector 4721629
[ 77.623222] blk_update_request: I/O error, dev vdb, sector 4721884
[ 83.028309] blk_update_request: I/O error, dev vdb, sector 2099200
[ 83.029042] Buffer I/O error on dev dm-0, logical block 262144, lost sync
page write
[ 83.029942] JBD2: Error -5 detected when updating journal superblock for
dm-0-8.
[ 83.030781] Aborting journal on device dm-0-8.
[ 83.031350] blk_update_request: I/O error, dev vdb, sector 2099200
[ 83.032128] blk_update_request: I/O error, dev vdb, sector 2099200
[ 83.032832] Buffer I/O error on dev dm-0, logical block 262144, lost sync
page write
[ 83.033726] JBD2: Error -5 detected when updating journal superblock for
dm-0-8.
sudo touch /mnt/foo
[ 88.035532] EXT4-fs (dm-0): previous I/O error to superblock detected
[ 88.037457] blk_update_request: I/O error, dev vdb, sector 2048
[ 88.039019] blk_update_request: I/O error, dev vdb, sector 2048
[ 88.040554] Buffer I/O error on dev dm-0, logical block 0, lost sync page
write
[ 88.043134] EXT4-fs error (device dm-0): ext4_journal_check_start:56:
Detected aborted journal
[ 88.045469] EXT4-fs (dm-0): Remounting filesystem read-only
[ 88.046897] EXT4-fs (dm-0): previous I/O error to superblock detected
[ 88.048745] blk_update_request: I/O error, dev vdb, sector 2048
[ 88.050147] blk_update_request: I/O error, dev vdb, sector 2048
[ 88.051528] Buffer I/O error on dev dm-0, logical block 0, lost sync page
write
touch: cannot touch '/mnt/foo': Read-only file system
(The read-only remount is due to errors=remount-ro being the default
option and me waiting a bit before trying the touch; I can also touch
/mnt/foo if I'm quick enough.)
If I try to mount just /dev/vdb1 (instead of a kpartx mapping), I get
the same message as I already posted, even with a xenial image.
I just searched a bit and found this:
https://www.redhat.com/archives/dm-devel/2013-October/msg00086.html
So it does appear to be a bug in kpartx.
> However, "foo" does not actually appear on the underlying image, so
> maybe it's sometimes using the overlay or something.
No, you just probably ssh'd in and didn't see the I/O errors in the
kernel log. ;-)
So this is completely harmless.
Regards,
Christian
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