On 08/01/2012 09:07 PM, Jan Schmidt wrote: > On Wed, August 01, 2012 at 14:02 (+0200), Liu Bo wrote: >> On 08/01/2012 07:45 PM, Stefan Behrens wrote: >>> With commit acce952b0, btrfs was changed to flag the filesystem with >>> BTRFS_SUPER_FLAG_ERROR and switch to read-only mode after a fatal >>> error happened like a write I/O errors of all mirrors. >>> In such situations, on unmount, the superblock is written in >>> btrfs_error_commit_super(). This is done with the intention to be able >>> to evaluate the error flag on the next mount. A warning is printed >>> in this case during the next mount and the log tree is ignored. >>> >>> The issue is that it is possible that the superblock points to a root >>> that was not written (due to write I/O errors). >>> The result is that the filesystem cannot be mounted. btrfsck also does >>> not start and all the other btrfs-progs tools fail to start as well. >>> However, mount -o recovery is working well and does the right things >>> to recover the filesystem (i.e., don't use the log root, clear the >>> free space cache and use the next mountable root that is stored in the >>> root backup array). >>> >>> This patch removes the writing of the superblock when >>> BTRFS_SUPER_FLAG_ERROR is set, and removes the handling of the error >>> flag in the mount function. >>> >> >> Yes, I have to admit that this can be a serious problem. >> >> But we'll need to send the error flag stored in the super block into >> disk in the future so that the next mount can find it unstable and do >> fsck by itself maybe. > > Hum, that's possible. However, I neither see > > a) a safe way to get that flag to disk > > nor > > b) a situation where this flag would help. When we abort a transaction, we > just > roll everything back to the last commit, i.e. a consistent state. So if we > stop > writing a potentially corrupt super block, we should be fine anyway. Or am I > missing something? >
I'm just wondering if we can roll everything back well, why do we need fsck? thanks, liubo > -Jan > -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
