linux-kernel - Re: [PATCH v2 0/4] Add online file check feature

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Date:	Fri, 4 Dec 2015 08:40:15 -0800
From:	Greg KH <greg@...ah.com>
To:	Gang He <ghe@...e.com>
Cc:	akpm@...ux-foundation.org, ocfs2-devel@....oracle.com,
	Mark Fasheh <MFasheh@...e.com>, rgoldwyn@...e.de, pavel@....cz,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 0/4] Add online file check feature

On Fri, Dec 04, 2015 at 01:36:21AM -0700, Gang He wrote:
> Hi Greg,
> 
> 
> >>> 
> > On Wed, Dec 02, 2015 at 07:05:27PM -0700, Gang He wrote:
> >> Hello Pavel,
> >> 
> >> 
> >> 
> >> >>> 
> >> > On Wed 2015-10-28 14:25:57, 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
> >> >> 
> >> > 
> >> > Are you sure this is reasonable interface? I mean.... sysfs is
> >> > supposed to be one value per file. And I don't think its suitable for
> >> > running commands.
> >> Usually, the corrupted file (inode) should be rarely encountered for OCFS2 
> > file system, then
> >> lots of commands are executed via this interface with high performance is 
> > not expected by us.
> >> Second, after online file check is added, we also plan to add a mount option 
> > "error=fix", that means
> >> the file system can fix these errors automatically without a manual command 
> > triggering.
> > 
> > It's not a "performance" issue, it's a "sysfs files only have one value"
> > type thing.  Have two files, "inode_fix" and "inode_check" and then just
> > write the inode into them, no need to have a "verb <inode>" type parser.
> Current, we have three functional items "check, fix and set", in the future, maybe we can add more item.
> Then, for each functional item, we need to create a sys file and add related code (actual some code is duplicated),
> I prefer to one sys file to handle multiple sub-commands.

No, sorry, that is not how sysfs works.  Please use individual files,
again, sysfs is "one value per file" you should never have to write a
"parser" for a sysfs file either reading, or writing to it.

If you need additional things in the future, great, add new sysfs files,
that makes it the easiest way for your userspace tools to be able to
determine if that feature is present in the kernel or not, it does not
have to write a command that it doesn't know if the kernel can handle or
not.

thanks,

greg k-h
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