linux/Documentation/filesystems/ocfs2-online-filecheck.rst
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   1.. SPDX-License-Identifier: GPL-2.0
   2
   3=====================================
   4OCFS2 file system - online file check
   5=====================================
   6
   7This document will describe OCFS2 online file check feature.
   8
   9Introduction
  10============
  11OCFS2 is often used in high-availability systems. However, OCFS2 usually
  12converts the filesystem to read-only when encounters an error. This may not be
  13necessary, since turning the filesystem read-only would affect other running
  14processes as well, decreasing availability.
  15Then, a mount option (errors=continue) is introduced, which would return the
  16-EIO errno to the calling process and terminate further processing so that the
  17filesystem is not corrupted further. The filesystem is not converted to
  18read-only, and the problematic file's inode number is reported in the kernel
  19log. The user can try to check/fix this file via online filecheck feature.
  20
  21Scope
  22=====
  23This effort is to check/fix small issues which may hinder day-to-day operations
  24of a cluster filesystem by turning the filesystem read-only. The scope of
  25checking/fixing is at the file level, initially for regular files and eventually
  26to all files (including system files) of the filesystem.
  27
  28In case of directory to file links is incorrect, the directory inode is
  29reported as erroneous.
  30
  31This feature is not suited for extravagant checks which involve dependency of
  32other components of the filesystem, such as but not limited to, checking if the
  33bits for file blocks in the allocation has been set. In case of such an error,
  34the offline fsck should/would be recommended.
  35
  36Finally, such an operation/feature should not be automated lest the filesystem
  37may end up with more damage than before the repair attempt. So, this has to
  38be performed using user interaction and consent.
  39
  40User interface
  41==============
  42When there are errors in the OCFS2 filesystem, they are usually accompanied
  43by the inode number which caused the error. This inode number would be the
  44input to check/fix the file.
  45
  46There is a sysfs directory for each OCFS2 file system mounting::
  47
  48  /sys/fs/ocfs2/<devname>/filecheck
  49
  50Here, <devname> indicates the name of OCFS2 volume device which has been already
  51mounted. The file above would accept inode numbers. This could be used to
  52communicate with kernel space, tell which file(inode number) will be checked or
  53fixed. Currently, three operations are supported, which includes checking
  54inode, fixing inode and setting the size of result record history.
  55
  561. If you want to know what error exactly happened to <inode> before fixing, do::
  57
  58    # echo "<inode>" > /sys/fs/ocfs2/<devname>/filecheck/check
  59    # cat /sys/fs/ocfs2/<devname>/filecheck/check
  60
  61The output is like this::
  62
  63    INO         DONE    ERROR
  64    39502               1       GENERATION
  65
  66    <INO> lists the inode numbers.
  67    <DONE> indicates whether the operation has been finished.
  68    <ERROR> says what kind of errors was found. For the detailed error numbers,
  69    please refer to the file linux/fs/ocfs2/filecheck.h.
  70
  712. If you determine to fix this inode, do::
  72
  73    # echo "<inode>" > /sys/fs/ocfs2/<devname>/filecheck/fix
  74    # cat /sys/fs/ocfs2/<devname>/filecheck/fix
  75
  76The output is like this:::
  77
  78    INO         DONE    ERROR
  79    39502               1       SUCCESS
  80
  81This time, the <ERROR> column indicates whether this fix is successful or not.
  82
  833. The record cache is used to store the history of check/fix results. It's
  84default size is 10, and can be adjust between the range of 10 ~ 100. You can
  85adjust the size like this::
  86
  87  # echo "<size>" > /sys/fs/ocfs2/<devname>/filecheck/set
  88
  89Fixing stuff
  90============
  91On receiving the inode, the filesystem would read the inode and the
  92file metadata. In case of errors, the filesystem would fix the errors
  93and report the problems it fixed in the kernel log. As a precautionary measure,
  94the inode must first be checked for errors before performing a final fix.
  95
  96The inode and the result history will be maintained temporarily in a
  97small linked list buffer which would contain the last (N) inodes
  98fixed/checked, the detailed errors which were fixed/checked are printed in the
  99kernel log.
 100