Re: [patch] loop.c to use write ops for fs requiring special locking

[Anton Altaparmakov <aia21@cam.ac.uk>]

On Fri, 10 Mar 2006, Andrew Morton wrote:
> Robert S Peterson <rpeterso@redhat.com> wrote:
> > On Thu, 2006-03-02 at 10:16 +0000, Anton Altaparmakov wrote:
> > > It is simply that it is faster on all file systems that can use 
> > > prepare_write/commit_write and the "performance hungry" would have 
> > > complained if it were to be removed.
> > (snip)
> > > 	Anton
> > 
> > Having heard no objections to my loop.c patch, when can I expect it to
> > be integrated into the 2.6 kernel?
> 
> When we've remembered what Al's statement meant in
> http://marc.theaimsgroup.com/?t=102129995600002&r=1&w=2
> 
> I knew at the time, but I've forgotten.  Maybe the issue went away..

The comment is that the patch put forward by Urban in the above thread 
replaced the use of readpage for reading with file ->read and 
prepare_write/commit_write for writing with file ->write without thinking 
about it.  So he left out the entire transformation on the data which is 
what Al correctly complained about.

I.e. Urban's patch made loop only work for a "straight" loopback mount 
without any changes to the data (i.e. crypto) applied to it.

This is no longer relevant because my patch which is in current 2.6 
kernels (can't remember when I wrote it/when it got put into 2.6) did the 
conversion from prepare_write/commit_write to file ->write correctly so 
the data transformation still happens so that crypto still works with the 
loop driver.

To get back to Robert's patch that he is requesting to be included.  I 
think it is fine but the flag name could perhaps be better.  Perhaps 
"FS_AOPS_PRIVATE" or "FS_AOPS_SPECIAL" or "FS_AOPS_NEED_LOCKING" or 
even "FS_AOPS_REQUIRE_LOCKING" or something.  "FS_REQUIRES_LOCKING" just 
does not mean much and certainly would not suggest to me that no-one 
outside the file system should use the address space operations of the 
file system...  But maybe I am just bein picky.  (-:

Best regards,

	Anton
-- 
Anton Altaparmakov <aia21 at cam.ac.uk> (replace at with @)
Unix Support, Computing Service, University of Cambridge, CB2 3QH, UK
Linux NTFS maintainer / IRC: #ntfs on irc.freenode.net
WWW: http://linux-ntfs.sf.net/ & http://www-stu.christs.cam.ac.uk/~aia21/