From d750c42ac265c00df3f0963a240a4440fa073603 Mon Sep 17 00:00:00 2001 From: Gang He Date: Tue, 22 Mar 2016 14:24:33 -0700 Subject: ocfs2: add feature document for online file check This document will describe OCFS2 online file check feature. OCFS2 is often used in high-availaibility systems. However, OCFS2 usually converts the filesystem to read-only when encounters an error. This may not be necessary, since turning the filesystem read-only would affect other running processes as well, decreasing availability. Then, a mount option (errors=continue) is introduced, which would return the -EIO errno to the calling process and terminate furhter processing so that the filesystem is not corrupted further. The filesystem is not converted to read-only, and the problematic file's inode number is reported in the kernel log. The user can try to check/fix this file via online filecheck feature. Signed-off-by: Gang He Cc: Mark Fasheh Cc: Joel Becker Cc: Junxiao Bi Cc: Joseph Qi Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- .../filesystems/ocfs2-online-filecheck.txt | 94 ++++++++++++++++++++++ 1 file changed, 94 insertions(+) create mode 100644 Documentation/filesystems/ocfs2-online-filecheck.txt (limited to 'Documentation') diff --git a/Documentation/filesystems/ocfs2-online-filecheck.txt b/Documentation/filesystems/ocfs2-online-filecheck.txt new file mode 100644 index 000000000000..1ab07860430d --- /dev/null +++ b/Documentation/filesystems/ocfs2-online-filecheck.txt @@ -0,0 +1,94 @@ + OCFS2 online file check + ----------------------- + +This document will describe OCFS2 online file check feature. + +Introduction +============ +OCFS2 is often used in high-availaibility systems. However, OCFS2 usually +converts the filesystem to read-only when encounters an error. This may not be +necessary, since turning the filesystem read-only would affect other running +processes as well, decreasing availability. +Then, a mount option (errors=continue) is introduced, which would return the +-EIO errno to the calling process and terminate furhter processing so that the +filesystem is not corrupted further. The filesystem is not converted to +read-only, and the problematic file's inode number is reported in the kernel +log. The user can try to check/fix this file via online filecheck feature. + +Scope +===== +This effort is to check/fix small issues which may hinder day-to-day operations +of a cluster filesystem by turning the filesystem read-only. The scope of +checking/fixing is at the file level, initially for regular files and eventually +to all files (including system files) of the filesystem. + +In case of directory to file links is incorrect, the directory inode is +reported as erroneous. + +This feature is not suited for extravagant checks which involve dependency of +other components of the filesystem, such as but not limited to, checking if the +bits for file blocks in the allocation has been set. In case of such an error, +the offline fsck should/would be recommended. + +Finally, such an operation/feature should not be automated lest the filesystem +may end up with more damage than before the repair attempt. So, this has to +be performed using user interaction and consent. + +User interface +============== +When there are errors in the OCFS2 filesystem, they are usually accompanied +by the inode number which caused the error. This inode number would be the +input to check/fix the file. + +There is a sysfs directory for each OCFS2 file system mounting: + + /sys/fs/ocfs2//filecheck + +Here, indicates the name of OCFS2 volumn device which has been already +mounted. The file above would accept inode numbers. This could be used to +communicate with kernel space, tell which file(inode number) will be checked or +fixed. Currently, three operations are supported, which includes checking +inode, fixing inode and setting the size of result record history. + +1. If you want to know what error exactly happened to before fixing, do + + # echo "" > /sys/fs/ocfs2//filecheck/check + # cat /sys/fs/ocfs2//filecheck/check + +The output is like this: + INO DONE ERROR +39502 1 GENERATION + + lists the inode numbers. + indicates whether the operation has been finished. + says what kind of errors was found. For the detailed error numbers, +please refer to the file linux/fs/ocfs2/filecheck.h. + +2. If you determine to fix this inode, do + + # echo "" > /sys/fs/ocfs2//filecheck/fix + # cat /sys/fs/ocfs2//filecheck/fix + +The output is like this: + INO DONE ERROR +39502 1 SUCCESS + +This time, the column indicates whether this fix is successful or not. + +3. The record cache is used to store the history of check/fix results. It's +defalut size is 10, and can be adjust between the range of 10 ~ 100. You can +adjust the size like this: + + # echo "" > /sys/fs/ocfs2//filecheck/set + +Fixing stuff +============ +On receivng the inode, the filesystem would read the inode and the +file metadata. In case of errors, the filesystem would fix the errors +and report the problems it fixed in the kernel log. As a precautionary measure, +the inode must first be checked for errors before performing a final fix. + +The inode and the result history will be maintained temporarily in a +small linked list buffer which would contain the last (N) inodes +fixed/checked, the detailed errors which were fixed/checked are printed in the +kernel log. -- cgit v1.2.3-59-g8ed1b