I just encountered some odd behavior from mkbtrfs.
The end goal is to restore a backup to newly created BTRFS partitions while
using the latest btrfs-tools.
Here''s the steps to what I did:
* Booted SystemRescueCD
* Partitioned the drives (two 750GB drives with 12 partitions each)
* Created an extra partition on sda as a temporary holding place for the backed
up files and so I can update btrfs-tools
* Formatted/mounted/restored backup files to the temporary partition which I
mounted on /mnt/backup
* mount -t proc none /mnt/backup/proc; mount -o bind /dev /mnt/backup/dev
* chroot /mnt/backup /bin/bash
* Updated btrfs-tools to the latest git pull from today
(v0.19-35-g1b444cd-dirty).
* mkbtrfs /dev/sda5 /dev/sdb5 -L root
mkbtrfs returned with:
error checking /dev/sda5 mount status
So I used strace to find out how it was checking for the mount status. Now,
I''m no expert here, but I''m confused as to just why it failed.
The last thing of note:
lstat("/boot", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
lstat("/boot/sysrcd.dat", 0x7fffb29681e0) = -1 ENOENT (No such file or
directory)
close(3) = 0
munmap(0x7f11df372000, 4096) = 0
write(2, "error checking /dev/sda5 mount s"..., 38error checking
/dev/sda5 mount status
) = 38
doesn''t explain much. I see that it''s checking /proc/mounts to
see what''s mounted, and then it fails on stating /boot/sysrcd.dat
(which doesn''t exist in the non-chrooted FS, btw).
To make this even weirder, if I format sda5/sdb5 using the SysRescCD version of
mkbtrfs (v0.19) and then format sda5/sdb5 using the chroot version, it works
fine.
Any ideas here? I would expect that mkbtrfs would work inside of a chroot
without any assistance from the original root.
I have the full strace from the chrooted mkbtrfs failing and from it succeeding,
if that''s helpful.
.:Justin:.
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Did you try using -o bind on /proc and /sys as well? Just in case mkfs uses /sys too, I''m not sure if /proc reacts differently to multiple mounts or bind neither? Envoyé de mon appareil mobile. Jérôme Poulin Solutions G.A. On 2011-01-02, at 14:53, J G <yoosty_cmn@yahoo.com> wrote:> I just encountered some odd behavior from mkbtrfs. > The end goal is to restore a backup to newly created BTRFS partitions while using the latest btrfs-tools. > Here''s the steps to what I did: > * Booted SystemRescueCD > * Partitioned the drives (two 750GB drives with 12 partitions each) > * Created an extra partition on sda as a temporary holding place for the backed up files and so I can update btrfs-tools > * Formatted/mounted/restored backup files to the temporary partition which I mounted on /mnt/backup > * mount -t proc none /mnt/backup/proc; mount -o bind /dev /mnt/backup/dev > * chroot /mnt/backup /bin/bash > * Updated btrfs-tools to the latest git pull from today (v0.19-35-g1b444cd-dirty). > * mkbtrfs /dev/sda5 /dev/sdb5 -L root > > mkbtrfs returned with: > > error checking /dev/sda5 mount status > > So I used strace to find out how it was checking for the mount status. Now, I''m no expert here, but I''m confused as to just why it failed. The last thing of note: > > lstat("/boot", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0 > lstat("/boot/sysrcd.dat", 0x7fffb29681e0) = -1 ENOENT (No such file or directory) > close(3) = 0 > munmap(0x7f11df372000, 4096) = 0 > write(2, "error checking /dev/sda5 mount s"..., 38error checking /dev/sda5 mount status > ) = 38 > > > doesn''t explain much. I see that it''s checking /proc/mounts to see what''s mounted, and then it fails on stating /boot/sysrcd.dat (which doesn''t exist in the non-chrooted FS, btw). > > To make this even weirder, if I format sda5/sdb5 using the SysRescCD version of mkbtrfs (v0.19) and then format sda5/sdb5 using the chroot version, it works fine. > > Any ideas here? I would expect that mkbtrfs would work inside of a chroot without any assistance from the original root. > > I have the full strace from the chrooted mkbtrfs failing and from it succeeding, if that''s helpful. > > > .:Justin:. > > > > -- > To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html-- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On 01/02/2011 08:52 PM, J G wrote:> I just encountered some odd behavior from mkbtrfs. > The end goal is to restore a backup to newly created BTRFS partitions while using the latest btrfs-tools. > Here''s the steps to what I did: > * Booted SystemRescueCD > * Partitioned the drives (two 750GB drives with 12 partitions each) > * Created an extra partition on sda as a temporary holding place for the backed up files and so I can update btrfs-tools > * Formatted/mounted/restored backup files to the temporary partition which I mounted on /mnt/backup > * mount -t proc none /mnt/backup/proc; mount -o bind /dev /mnt/backup/dev > * chroot /mnt/backup /bin/bash > * Updated btrfs-tools to the latest git pull from today (v0.19-35-g1b444cd-dirty). > * mkbtrfs /dev/sda5 /dev/sdb5 -L root > > mkbtrfs returned with: > > error checking /dev/sda5 mount status > > So I used strace to find out how it was checking for the mount status. Now, I''m no expert here, but I''m confused as to just why it failed. The last thing of note: > > lstat("/boot", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0 > lstat("/boot/sysrcd.dat", 0x7fffb29681e0) = -1 ENOENT (No such file or directory) > close(3) = 0 > munmap(0x7f11df372000, 4096) = 0 > write(2, "error checking /dev/sda5 mount s"..., 38error checking /dev/sda5 mount status > ) = 38 > > > doesn''t explain much. I see that it''s checking /proc/mounts to see what''s mounted, and then it fails on stating /boot/sysrcd.dat (which doesn''t exist in the non-chrooted FS, btw). > > To make this even weirder, if I format sda5/sdb5 using the SysRescCD version of mkbtrfs (v0.19) and then format sda5/sdb5 using the chroot version, it works fine. > > Any ideas here? I would expect that mkbtrfs would work inside of a chroot without any assistance from the original root. > > I have the full strace from the chrooted mkbtrfs failing and from it succeeding, if that''s helpful.On the basis of the provided information, and on the code it seems that mkfs.btrfs tries hard to check that the user is not formatting a mounted disk (or loop). So mkfs.btrfs scan the /proc/mount file and checks every devices. To do the check it needs to access the original file if this is a "loop backend". This is reasonable. In this case in a chroot-ed environment the loop file is not accessible. If you need a [dirty] "quick hack" to by-pass the problem (not tested): - unmount the proc filesystem - create an empty file /proc/mounts - run btrfs.fsck - mount the proc filesystem (removing the fake mounts file) - perform a "btrfs device scan" - mount the filesystem Of course the "right" solution is to add a "--force" switch which permits to by-pass these checks. Other mkfs.* tools have this switch. From the mkfs.ext4 man page: [...] -F Force mke2fs to create a filesystem, even if the specified device is not a partition on a block special device, or if other parameters do not make sense. In order to force mke2fs to create a filesystem even if the filesystem appears to be in use or is mounted (a truly dangerous thing to do), this option must be specified twice. [...]> > .:Justin:. > > > > -- > To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > . >-- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Goffredo Baroncelli
2011-Jan-03 19:05 UTC
[PATCH] add a --force option to mkfs.btrf [was Re: Odd mkbtrfs behavior inside of chroot]
-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Hi all and happy new year. this is my first patch of the new year. Hooping that this is a good sign. :-) The enclosed patch try to address the problem raised by Justin: how circumvent the check performed by mkfs.btrfs ? I add a "-f|--force" switch which permits to bypass the check if a device is already mounted. I update the man page too. You can pull the change from http://cassiopea.homelinux.net/git/btrfs-progs-unstable.git branch force-mkfs commit (2900a150cde604f82f1437c931792bfa59c4780b) Comments are welcome Regards G.Baroncelli - -- gpg key: Goffredo Baroncelli (ghigo) <kreijack@inwind.it> Key fingerprint = 4769 7E51 5293 D36C 814E C054 BF04 F161 3DC5 0512 On 01/03/2011 12:14 AM, Goffredo Baroncelli wrote:> On 01/02/2011 08:52 PM, J G wrote: >> I just encountered some odd behavior from mkbtrfs. >> The end goal is to restore a backup to newly created BTRFS partitions while using the latest btrfs-tools. >> Here''s the steps to what I did: >> * Booted SystemRescueCD >> * Partitioned the drives (two 750GB drives with 12 partitions each) >> * Created an extra partition on sda as a temporary holding place for the backed up files and so I can update btrfs-tools >> * Formatted/mounted/restored backup files to the temporary partition which I mounted on /mnt/backup >> * mount -t proc none /mnt/backup/proc; mount -o bind /dev /mnt/backup/dev >> * chroot /mnt/backup /bin/bash >> * Updated btrfs-tools to the latest git pull from today (v0.19-35-g1b444cd-dirty). >> * mkbtrfs /dev/sda5 /dev/sdb5 -L root >> >> mkbtrfs returned with: >> >> error checking /dev/sda5 mount status >> >> So I used strace to find out how it was checking for the mount status. Now, I''m no expert here, but I''m confused as to just why it failed. The last thing of note: >> >> lstat("/boot", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0 >> lstat("/boot/sysrcd.dat", 0x7fffb29681e0) = -1 ENOENT (No such file or directory) >> close(3) = 0 >> munmap(0x7f11df372000, 4096) = 0 >> write(2, "error checking /dev/sda5 mount s"..., 38error checking /dev/sda5 mount status >> ) = 38 >> >> >> doesn''t explain much. I see that it''s checking /proc/mounts to see what''s mounted, and then it fails on stating /boot/sysrcd.dat (which doesn''t exist in the non-chrooted FS, btw). >> >> To make this even weirder, if I format sda5/sdb5 using the SysRescCD version of mkbtrfs (v0.19) and then format sda5/sdb5 using the chroot version, it works fine. >> >> Any ideas here? I would expect that mkbtrfs would work inside of a chroot without any assistance from the original root. >> >> I have the full strace from the chrooted mkbtrfs failing and from it succeeding, if that''s helpful. > > On the basis of the provided information, and on the code it seems that > mkfs.btrfs tries hard to check that the user is not formatting a mounted > disk (or loop). So mkfs.btrfs scan the /proc/mount file and checks every > devices. To do the check it needs to access the original file if this is > a "loop backend". This is reasonable. > > In this case in a chroot-ed environment the loop file is not accessible. > > If you need a [dirty] "quick hack" to by-pass the problem (not tested): > - unmount the proc filesystem > - create an empty file /proc/mounts > - run btrfs.fsck > - mount the proc filesystem (removing the fake mounts file) > - perform a "btrfs device scan" > - mount the filesystem > > Of course the "right" solution is to add a "--force" switch which > permits to by-pass these checks. Other mkfs.* tools have this switch. > >>From the mkfs.ext4 man page: > [...] > -F Force mke2fs to create a filesystem, > even if the specified device is not > a partition on a block special > device, or if other parameters do > not make sense. In order to force > mke2fs to create a filesystem even > if the filesystem appears to be in > use or is mounted (a truly dangerous > thing to do), this option must be > specified twice. > > [...] > > >> >> .:Justin:. >> >> >> >> -- >> To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in >> the body of a message to majordomo@vger.kernel.org >> More majordomo info at http://vger.kernel.org/majordomo-info.html >> . >> > > -- > To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > . >-----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.10 (GNU/Linux) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org/ iD8DBQFNIh34vwTxYT3FBRIRAl1tAJ9k1LVUfahdlvLvK7b4gct55fom3QCfd1Ab 0JfVbWgKf7DXd0Gg1YzaPdU=Jt+e -----END PGP SIGNATURE-----
Binding /sys proved futile. .:Justin:. --- On Sun, 1/2/11, Jérôme Poulin <jeromepoulin@gmail.com> wrote:> From: Jérôme Poulin <jeromepoulin@gmail.com> > Subject: Re: Odd mkbtrfs behavior inside of chroot > To: "J G" <yoosty_cmn@yahoo.com> > Cc: "linux-btrfs@vger.kernel.org" <linux-btrfs@vger.kernel.org> > Date: Sunday, January 2, 2011, 1:06 PM > Did you try using -o bind on /proc > and /sys as well? Just in case mkfs > uses /sys too, I''m not sure if /proc reacts differently to > multiple > mounts or bind neither? > > Envoyé de mon appareil mobile. > > Jérôme Poulin > Solutions G.A. > > On 2011-01-02, at 14:53, J G <yoosty_cmn@yahoo.com> > wrote: > > > I just encountered some odd behavior from mkbtrfs. > > The end goal is to restore a backup to newly created > BTRFS partitions while using the latest btrfs-tools. > > Here''s the steps to what I did: > > * Booted SystemRescueCD > > * Partitioned the drives (two 750GB drives with 12 > partitions each) > > * Created an extra partition on sda as a temporary > holding place for the backed up files and so I can update > btrfs-tools > > * Formatted/mounted/restored backup files to the > temporary partition which I mounted on /mnt/backup > > * mount -t proc none /mnt/backup/proc; mount -o bind > /dev /mnt/backup/dev > > * chroot /mnt/backup /bin/bash > > * Updated btrfs-tools to the latest git pull from > today (v0.19-35-g1b444cd-dirty). > > * mkbtrfs /dev/sda5 /dev/sdb5 -L root > > > > mkbtrfs returned with: > > > > error checking /dev/sda5 mount status > > > > So I used strace to find out how it was checking for > the mount status. Now, I''m no expert here, but I''m confused > as to just why it failed. The last thing of note: > > > > lstat("/boot", {st_mode=S_IFDIR|0755, st_size=4096, > ...}) = 0 > > lstat("/boot/sysrcd.dat", 0x7fffb29681e0) = -1 ENOENT > (No such file or directory) > > close(3) > > = 0 > > munmap(0x7f11df372000, 4096) > = 0 > > write(2, "error checking /dev/sda5 mount s"..., > 38error checking /dev/sda5 mount status > > ) = 38 > > > > > > doesn''t explain much. I see that it''s checking > /proc/mounts to see what''s mounted, and then it fails on > stating /boot/sysrcd.dat (which doesn''t exist in the > non-chrooted FS, btw). > > > > To make this even weirder, if I format sda5/sdb5 using > the SysRescCD version of mkbtrfs (v0.19) and then format > sda5/sdb5 using the chroot version, it works fine. > > > > Any ideas here? I would expect that mkbtrfs would work > inside of a chroot without any assistance from the original > root. > > > > I have the full strace from the chrooted mkbtrfs > failing and from it succeeding, if that''s helpful. > > > > > > .:Justin:. > > > > > > > > -- > > To unsubscribe from this list: send the line > "unsubscribe linux-btrfs" in > > the body of a message to majordomo@vger.kernel.org > > More majordomo info at http://vger.kernel.org/majordomo-info.html >-- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
You''re little trick with touching a blank /proc/mounts works, FWIW. You''re "--force" patch works even better however ;) Thanks! .:Justin:. --- On Sun, 1/2/11, Goffredo Baroncelli <kreijack@libero.it> wrote:> From: Goffredo Baroncelli <kreijack@libero.it> > Subject: Re: Odd mkbtrfs behavior inside of chroot > To: "J G" <yoosty_cmn@yahoo.com> > Cc: linux-btrfs@vger.kernel.org > Date: Sunday, January 2, 2011, 3:14 PM > On 01/02/2011 08:52 PM, J G wrote: > > I just encountered some odd behavior from mkbtrfs. > > The end goal is to restore a backup to newly created > BTRFS partitions while using the latest btrfs-tools. > > Here''s the steps to what I did: > > * Booted SystemRescueCD > > * Partitioned the drives (two 750GB drives with 12 > partitions each) > > * Created an extra partition on sda as a temporary > holding place for the backed up files and so I can update > btrfs-tools > > * Formatted/mounted/restored backup files to the > temporary partition which I mounted on /mnt/backup > > * mount -t proc none /mnt/backup/proc; mount -o bind > /dev /mnt/backup/dev > > * chroot /mnt/backup /bin/bash > > * Updated btrfs-tools to the latest git pull from > today (v0.19-35-g1b444cd-dirty). > > * mkbtrfs /dev/sda5 /dev/sdb5 -L root > > > > mkbtrfs returned with: > > > > error checking /dev/sda5 mount status > > > > So I used strace to find out how it was checking for > the mount status. Now, I''m no expert here, but I''m confused > as to just why it failed. The last thing of note: > > > > lstat("/boot", {st_mode=S_IFDIR|0755, st_size=4096, > ...}) = 0 > > lstat("/boot/sysrcd.dat", 0x7fffb29681e0) = -1 ENOENT > (No such file or directory) > > close(3) > > = 0 > > munmap(0x7f11df372000, 4096) > = 0 > > write(2, "error checking /dev/sda5 mount s"..., > 38error checking /dev/sda5 mount status > > ) = 38 > > > > > > doesn''t explain much. I see that it''s checking > /proc/mounts to see what''s mounted, and then it fails on > stating /boot/sysrcd.dat (which doesn''t exist in the > non-chrooted FS, btw). > > > > To make this even weirder, if I format sda5/sdb5 using > the SysRescCD version of mkbtrfs (v0.19) and then format > sda5/sdb5 using the chroot version, it works fine. > > > > Any ideas here? I would expect that mkbtrfs would work > inside of a chroot without any assistance from the original > root. > > > > I have the full strace from the chrooted mkbtrfs > failing and from it succeeding, if that''s helpful. > > On the basis of the provided information, and on the code > it seems that > mkfs.btrfs tries hard to check that the user is not > formatting a mounted > disk (or loop). So mkfs.btrfs scan the /proc/mount file and > checks every > devices. To do the check it needs to access the original > file if this is > a "loop backend". This is reasonable. > > In this case in a chroot-ed environment the loop file is > not accessible. > > If you need a [dirty] "quick hack" to by-pass the problem > (not tested): > - unmount the proc filesystem > - create an empty file /proc/mounts > - run btrfs.fsck > - mount the proc filesystem (removing the fake mounts > file) > - perform a "btrfs device scan" > - mount the filesystem > > Of course the "right" solution is to add a "--force" switch > which > permits to by-pass these checks. Other mkfs.* tools have > this switch. > > From the mkfs.ext4 man page: > [...] > -F > Force mke2fs to create a filesystem, > even if > the specified device is not > > a partition on a > block special > device, or > if other parameters do > not > make sense. In order to force > mke2fs to > create a filesystem even > if > the filesystem appears to be in > use or is > mounted (a truly dangerous > > thing to do), this option must be > specified > twice. > > [...] > > > > > > .:Justin:. > > > > > > > > -- > > To unsubscribe from this list: send the line > "unsubscribe linux-btrfs" in > > the body of a message to majordomo@vger.kernel.org > > More majordomo info at http://vger.kernel.org/majordomo-info.html > > . > > > >-- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html