Re: synchronous mounts

[Andrew Morton <akpm@zip.com.au>]

"Stephen C. Tweedie" wrote:
> 
> Hi,
> 
> On Thu, Nov 15, 2001 at 12:03:57AM -0800, Andrew Morton wrote:
> > Linux is not syncing write() data for files on synchronously mounted
> > filesystems, and it isn't syncing write() data for ext2/3 files which
> > are operating under `chattr +S'.
> 
> In the past, chattr +S and mount -o sync always resulted in sync
> metadata with no guarantees about data.
> 
> I'm not sure this makes much sense, but it's what has always happened.
> For directories, the behaviour is fine, in particular as it gives us
> the same directory sync consistency semantics as synchronous BSD UFS.
> 
> It's not clear to me that chattr/mount sync options make _any_ sense
> for regular file metadata.  Rather than tightening up the semantics,
> I'd actually prefer to restrict them so that they only apply to
> directories.  Users who set the sync bits are usually doing so for
> applications like MTAs where it's directory syncing which is
> what matters: the apps typically fsync the files themselves, anyway.
> 

OK, that makes sense.  Thanks.  The `mount' and `chattr' manpages
need updating...

So shall we try to nail this down?  Synchronous mounts and chattr +S
provide synchronous semantics for directory contents, diretory metadata
and directory inodes only.  And fsync() will write out a file's data,
metadata and inode?

If this is correct then there are a few places where ext2 is
syncing stuff unnecessarily - file indirect blocks, etc.  Not
very important at this stage I guess.

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