| Message ID | 1374773376-29853-2-git-send-email-anand.jain@oracle.com (mailing list archive) |
|---|---|
| State | Superseded, archived |
| Headers | show |
On 7/25/13 12:29 PM, Anand Jain wrote: > There is a very less chance that all the copies of SB > on the disk is zeroed unintentionally. unless device > is removed, so this fix will ensure all copies on the > disk is zeroed when the disk is intentionally removed. > > reproducer: > ------------------- > btrfs dev del /dev/sdc /btrfs > echo $? > 0 > umount /btrfs > btrfs fi show > Label: none uuid: e7aae9f0-1aa8-41f5-8fb6-d4d8f80cdb2c > Total devices 1 FS bytes used 28.00KiB > devid 1 size 2.00GiB used 20.00MiB path /dev/sdb Great, so dev del makes it unfindable . . . > ./btrfs-select-super -s 1 /dev/sdc > using SB copy 1, bytenr 67108864 Now you use a rescue tool to resurrect the fs from a backup superblock. And: > btrfs fi show > Label: none uuid: e7aae9f0-1aa8-41f5-8fb6-d4d8f80cdb2c > Total devices 1 FS bytes used 28.00KiB > devid 2 size 2.00GiB used 0.00 path /dev/sdc <-- WRONG > devid 1 size 2.00GiB used 20.00MiB path /dev/sdb Ok, now it's findable. Isn't that exactly how this should behave? What is wrong about this? > mount /dev/sdc /btrfs > btrfs fi show --kernel > Label: none uuid: e7aae9f0-1aa8-41f5-8fb6-d4d8f80cdb2c mounted: /btrfs > Group profile: metadata: single data: single > Total devices 1 FS bytes used 28.00KiB > devid 1 size 2.00GiB used 20.00MiB path /dev/sdb Oh good, you could bring it back after a potential administrative error, using a recovery tool (btrfs-select-super)! Isn't that a good thing? IOWS: what does this change actually fix? -Eric > --------------------- > > Signed-off-by: Anand Jain <anand.jain@oracle.com> > --- > fs/btrfs/volumes.c | 30 ++++++++++++++++++++++++++++++ > 1 files changed, 30 insertions(+), 0 deletions(-) > > diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c > index 557a743..090f57c 100644 > --- a/fs/btrfs/volumes.c > +++ b/fs/btrfs/volumes.c > @@ -1641,12 +1641,42 @@ int btrfs_rm_device(struct btrfs_root *root, char *device_path) > * remove it from the devices list and zero out the old super > */ > if (clear_super && disk_super) { > + u64 bytenr; > + int i; > + > /* make sure this device isn't detected as part of > * the FS anymore > */ > memset(&disk_super->magic, 0, sizeof(disk_super->magic)); > set_buffer_dirty(bh); > sync_dirty_buffer(bh); > + > + /* clear the mirror copies of super block on the disk > + * being removed, 0th copy is been taken care above and > + * the below would take of the rest > + */ > + for (i = 1; i < BTRFS_SUPER_MIRROR_MAX; i++) { > + brelse(bh); > + bytenr = btrfs_sb_offset(i); > + if (bytenr + BTRFS_SUPER_INFO_SIZE >= > + i_size_read(bdev->bd_inode)) > + break; > + bh = __bread(bdev, bytenr / 4096, > + BTRFS_SUPER_INFO_SIZE); > + if (!bh) > + continue; > + > + disk_super = (struct btrfs_super_block *)bh->b_data; > + > + if (btrfs_super_bytenr(disk_super) != bytenr || > + btrfs_super_magic(disk_super) != BTRFS_MAGIC) { > + continue; > + } > + memset(&disk_super->magic, 0, > + sizeof(disk_super->magic)); > + set_buffer_dirty(bh); > + sync_dirty_buffer(bh); > + } > } > > ret = 0; > -- 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
>> btrfs fi show >> Label: none uuid: e7aae9f0-1aa8-41f5-8fb6-d4d8f80cdb2c >> Total devices 1 FS bytes used 28.00KiB >> devid 2 size 2.00GiB used 0.00 path /dev/sdc <-- WRONG >> devid 1 size 2.00GiB used 20.00MiB path /dev/sdb > > Ok, now it's findable. Isn't that exactly how this should behave? > What is wrong about this? Total devices is still 1. >> mount /dev/sdc /btrfs >> btrfs fi show --kernel >> Label: none uuid: e7aae9f0-1aa8-41f5-8fb6-d4d8f80cdb2c mounted: /btrfs >> Group profile: metadata: single data: single >> Total devices 1 FS bytes used 28.00KiB >> devid 1 size 2.00GiB used 20.00MiB path /dev/sdb > > Oh good, you could bring it back after a potential administrative error, > using a recovery tool (btrfs-select-super)! Isn't that a good thing? Note, here btrfs fi show used the new option --kernel this does not show /dev/sdc though you use it mount. Its all messed up. If user wants to bring back the intentionally deleted disk, then they should rather call btrfs dev add, so that it will take care of integrating the disk back to the FS. recovery tools are for possible recovery from the corruption, delete is not a corruption. Thats an intentional step that user decided to take and the undo for it is 'dev add'. > IOWS: what does this change actually fix? Writes zeros to all copies of SB when disk is deleted (before we used to just zero only the first copy). In that way corruption is distinguished from the deleted disk in a fair calculations. Otherwise allowing these things would cost us in terms of support for the administrative error. Which we don't have to encourage. Thanks, Anand -- 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 8/9/13 9:04 PM, anand jain wrote: > > >>> btrfs fi show >>> Label: none uuid: e7aae9f0-1aa8-41f5-8fb6-d4d8f80cdb2c >>> Total devices 1 FS bytes used 28.00KiB >>> devid 2 size 2.00GiB used 0.00 path /dev/sdc <-- WRONG >>> devid 1 size 2.00GiB used 20.00MiB path /dev/sdb >> >> Ok, now it's findable. Isn't that exactly how this should behave? >> What is wrong about this? > > Total devices is still 1. Hm, so it is. But that inconsistency indicates a bug somewhere else, doesn't it? (FWIW the above works for me, w/ the right number of devices shown after removal...) Anyway, I wonder if we've ever resolved the "when should we look for backup superblocks?" question. Because that would inform decisions about when they should be read, when they must be zeroed, etc. I thought the plan was that backup superblocks should not be read unless we explicitly specify it via mount option or btrfs commandline option. If we must add code to zero all the superblocks on removal to fix something that's still discovering them, that seems to mean backups are still being automatically read. Should they be? What is the design intent for when backup SBs whould be used? Maybe then I could better understand the reason for this change. Thanks, -Eric >>> mount /dev/sdc /btrfs >>> btrfs fi show --kernel >>> Label: none uuid: e7aae9f0-1aa8-41f5-8fb6-d4d8f80cdb2c mounted: /btrfs >>> Group profile: metadata: single data: single >>> Total devices 1 FS bytes used 28.00KiB >>> devid 1 size 2.00GiB used 20.00MiB path /dev/sdb >> >> Oh good, you could bring it back after a potential administrative error, >> using a recovery tool (btrfs-select-super)! Isn't that a good thing? > > Note, here btrfs fi show used the new option --kernel > this does not show /dev/sdc though you use it mount. > Its all messed up. > > If user wants to bring back the intentionally deleted > disk, then they should rather call btrfs dev add, so > that it will take care of integrating the disk back > to the FS. > > recovery tools are for possible recovery from the > corruption, delete is not a corruption. Thats an > intentional step that user decided to take and the > undo for it is 'dev add'. > >> IOWS: what does this change actually fix? > > Writes zeros to all copies of SB when disk is deleted > (before we used to just zero only the first copy). > In that way corruption is distinguished from the > deleted disk in a fair calculations. > > Otherwise allowing these things would cost us in terms > of support for the administrative error. Which we don't > have to encourage. > > Thanks, Anand -- 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
Hi Eric, >>>> btrfs fi show >>>> Label: none uuid: e7aae9f0-1aa8-41f5-8fb6-d4d8f80cdb2c >>>> Total devices 1 FS bytes used 28.00KiB >>>> devid 2 size 2.00GiB used 0.00 path /dev/sdc <-- WRONG >>>> devid 1 size 2.00GiB used 20.00MiB path /dev/sdb >>> >>> Ok, now it's findable. Isn't that exactly how this should behave? >>> What is wrong about this? >> >> Total devices is still 1. > > Hm, so it is. But that inconsistency indicates a bug > somewhere else, doesn't it? Nope. to undo dev-delete admin has to use dev-add. Here the idea is to release the disk nicely when we know we don't need it anymore. Thanks, Anand -- 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
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c index 557a743..090f57c 100644 --- a/fs/btrfs/volumes.c +++ b/fs/btrfs/volumes.c @@ -1641,12 +1641,42 @@ int btrfs_rm_device(struct btrfs_root *root, char *device_path) * remove it from the devices list and zero out the old super */ if (clear_super && disk_super) { + u64 bytenr; + int i; + /* make sure this device isn't detected as part of * the FS anymore */ memset(&disk_super->magic, 0, sizeof(disk_super->magic)); set_buffer_dirty(bh); sync_dirty_buffer(bh); + + /* clear the mirror copies of super block on the disk + * being removed, 0th copy is been taken care above and + * the below would take of the rest + */ + for (i = 1; i < BTRFS_SUPER_MIRROR_MAX; i++) { + brelse(bh); + bytenr = btrfs_sb_offset(i); + if (bytenr + BTRFS_SUPER_INFO_SIZE >= + i_size_read(bdev->bd_inode)) + break; + bh = __bread(bdev, bytenr / 4096, + BTRFS_SUPER_INFO_SIZE); + if (!bh) + continue; + + disk_super = (struct btrfs_super_block *)bh->b_data; + + if (btrfs_super_bytenr(disk_super) != bytenr || + btrfs_super_magic(disk_super) != BTRFS_MAGIC) { + continue; + } + memset(&disk_super->magic, 0, + sizeof(disk_super->magic)); + set_buffer_dirty(bh); + sync_dirty_buffer(bh); + } } ret = 0;
There is a very less chance that all the copies of SB on the disk is zeroed unintentionally. unless device is removed, so this fix will ensure all copies on the disk is zeroed when the disk is intentionally removed. reproducer: ------------------- btrfs dev del /dev/sdc /btrfs echo $? 0 umount /btrfs btrfs fi show Label: none uuid: e7aae9f0-1aa8-41f5-8fb6-d4d8f80cdb2c Total devices 1 FS bytes used 28.00KiB devid 1 size 2.00GiB used 20.00MiB path /dev/sdb ./btrfs-select-super -s 1 /dev/sdc using SB copy 1, bytenr 67108864 btrfs fi show Label: none uuid: e7aae9f0-1aa8-41f5-8fb6-d4d8f80cdb2c Total devices 1 FS bytes used 28.00KiB devid 2 size 2.00GiB used 0.00 path /dev/sdc <-- WRONG devid 1 size 2.00GiB used 20.00MiB path /dev/sdb mount /dev/sdc /btrfs btrfs fi show --kernel Label: none uuid: e7aae9f0-1aa8-41f5-8fb6-d4d8f80cdb2c mounted: /btrfs Group profile: metadata: single data: single Total devices 1 FS bytes used 28.00KiB devid 1 size 2.00GiB used 20.00MiB path /dev/sdb --------------------- Signed-off-by: Anand Jain <anand.jain@oracle.com> --- fs/btrfs/volumes.c | 30 ++++++++++++++++++++++++++++++ 1 files changed, 30 insertions(+), 0 deletions(-)