Message-Id: <55ACF3C9020000F90000F31C@relay2.provo.novell.com>
Date:	Sun, 19 Jul 2015 23:12:41 -0600
From:	"Gang He" <ghe@...e.com>
To:	"Gang He" <GHe@...e.com>, "Mark Fasheh" <MFasheh@...e.com>,
	<rgoldwyn@...e.de>
Cc:	<akpm@...ux-foundation.org>, <ocfs2-devel@....oracle.com>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ocfs2: add feature document for online file check

Hello Andrew/Mark/Goldwyn,

The doc describes OCFS2 online file check feature, which is added by the last suggestion when I submitted a few online file check code patches.
Online file check patches link:
https://oss.oracle.com/pipermail/ocfs2-devel/2015-June/010886.html 
https://oss.oracle.com/pipermail/ocfs2-devel/2015-June/010885.html 
https://oss.oracle.com/pipermail/ocfs2-devel/2015-June/010888.html 
https://oss.oracle.com/pipermail/ocfs2-devel/2015-June/010887.html 
https://oss.oracle.com/pipermail/ocfs2-devel/2015-June/010889.html 


Thanks
Gang


>>> 
> 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 on errors. 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) was 
> introduced,
> which would return the EIO 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 <ghe@...e.com>
> ---
>  .../filesystems/ocfs2-online-filecheck.txt         | 95 
> ++++++++++++++++++++++
>  1 file changed, 95 insertions(+)
>  create mode 100644 Documentation/filesystems/ocfs2-online-filecheck.txt
> 
> diff --git a/Documentation/filesystems/ocfs2-online-filecheck.txt 
> b/Documentation/filesystems/ocfs2-online-filecheck.txt
> new file mode 100644
> index 0000000..d319237
> --- /dev/null
> +++ b/Documentation/filesystems/ocfs2-online-filecheck.txt
> @@ -0,0 +1,95 @@
> +		    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 on errors. 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) was 
> introduced,
> +which would return the EIO 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 file for each OCFS2 file system mounting:
> +
> +  /sys/fs/ocfs2/<devname>/filecheck
> +
> +Here, <devname> 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 <inode> before fixing, 
> do
> +
> +  # echo "CHECK <inode>" > /sys/fs/ocfs2/<devname>/filecheck
> +  # cat /sys/fs/ocfs2/<devname>/filecheck
> +
> +The output is like this:
> +  INO		TYPE		DONE		ERROR
> +39502		0		1		GENERATION
> +
> +<INO> lists the inode numbers.
> +<TYPE> is what kind of operation you've done, 0 for inode check,1 for inode 
> fix.
> +<DONE> indicates whether the operation has been finished.
> +<ERROR> 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 "FIX <inode>" > /sys/fs/ocfs2/<devname>/filecheck
> +  # cat /sys/fs/ocfs2/<devname>/filecheck
> +
> +The output is like this:
> +  INO		TYPE		DONE		ERROR
> +39502		1		1		SUCCESS
> +
> +This time, the <ERROR> column indicates whether this fix is successful or 
> not.
> +
> +3. The record cache is used to store the history of check/fix result. Its
> +defalut size is 10, and can be adjust between the range of 10 ~ 100. You 
> can
> +adjust the size like this:
> +
> +  # echo "SET <size>" > /sys/fs/ocfs2/<devname>/filecheck
> +
> +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.
> -- 
> 2.1.2
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