Re: [Ocfs2-devel] [PATCH v2 0/4] Add online file check feature

[Srinivas Eeda]

Hi Gang,

thanks for pointing to explanation of the feature.

What I am curious about is ... what were the real cases that you came 
across prompted this change and how this change would help in that case.

Thanks,
--Srini


On 10/28/2015 09:44 PM, Gang He wrote:
> Hello Srini,
>
> There is a doc about ocfs2 online file check.
>
> 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. So,the filesystem is
> not converted to read-only, and the problematic file's inode number is reported
> in the kernel log so that 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 details, 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 fix history will be maintained temporarily in a
> small linked list buffer which would contain the last (N) inodes
> fixed/checked, along with the logs of what errors were reported/fixed.
>
> Thanks
> Gang
>
>
> > Hi Gang,
> >
> > thank you for implementing this. I would like to understand this better
> > on where and how it helps ... would you mind sharing couple
> > examples(real scenarios).
> >
> > Thanks,
> > --Srini
> >
> >
> > On 10/27/2015 11:25 PM, Gang He wrote:
> > > 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 fixing the file.
> > > One of these options could be considered:
> > > A file in the sys filesytem which would accept inode numbers.
> > > This could be used to communication back what has to be fixed or is fixed.
> > > You could write:
> > > $# echo "CHECK <inode>" > /sys/fs/ocfs2/devname/filecheck
> > > or
> > > $# echo "FIX <inode>" > /sys/fs/ocfs2/devname/filecheck
> > >
> > > Compare with first version, I use strncasecmp instead of double strncmp
> > > functions. Second, update the source file contribution vendor.
> > >
> > > Gang He (4):
> > >     ocfs2: export ocfs2_kset for online file check
> > >     ocfs2: sysfile interfaces for online file check
> > >     ocfs2: create/remove sysfile for online file check
> > >     ocfs2: check/fix inode block for online file check
> > >
> > >    fs/ocfs2/Makefile      |   3 +-
> > >    fs/ocfs2/filecheck.c   | 566
> > +++++++++++++++++++++++++++++++++++++++++++++++++
> > >    fs/ocfs2/filecheck.h   |  48 +++++
> > >    fs/ocfs2/inode.c       | 196 ++++++++++++++++-
> > >    fs/ocfs2/inode.h       |   3 +
> > >    fs/ocfs2/ocfs2_trace.h |   2 +
> > >    fs/ocfs2/stackglue.c   |   3 +-
> > >    fs/ocfs2/stackglue.h   |   2 +
> > >    fs/ocfs2/super.c       |   5 +
> > >    9 files changed, 820 insertions(+), 8 deletions(-)
> > >    create mode 100644 fs/ocfs2/filecheck.c
> > >    create mode 100644 fs/ocfs2/filecheck.h

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