[patch 2.6.16] loop.c to use write ops for fs requiring special locking [try #2]

[Robert S Peterson <rpeterso@redhat.com>]

On Sat, 2006-03-11 at 00:36 +0000, Anton Altaparmakov wrote:
> On Fri, 10 Mar 2006, Andrew Morton wrote:
> > When we've remembered what Al's statement meant in
> > http://marc.theaimsgroup.com/?t=102129995600002&r=1&w=2
> 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.  (-:

Here is a resubmission of my patch to loop.c, this time against the
2.6.16 kernel.

Andrew: Sounds like Anton answered your concerns.
Anton:  As per your suggestion, I changed the constant to your suggested
FS_AOPS_NEED_LOCKING.

Regards,

Bob Peterson
rpeterso@redhat.com

diff -pur linux-2.6.16/drivers/block/loop.c linux-2.6.16.patched/drivers/block/loop.c
--- linux-2.6.16/drivers/block/loop.c   2006-03-19 23:53:29.000000000 -0600
+++ linux-2.6.16.patched/drivers/block/loop.c   2006-03-24 10:49:10.000000000 -0600
@@ -44,6 +44,11 @@
  * backing filesystem.
  * Anton Altaparmakov, 16 Feb 2005
  *
+ * Extension of Anton's idea: Use normal write file operations rather than
+ * prepare_write and commit_write when the backing filesystem requires
+ * special locking.
+ * Robert Peterson <rpeterso@redhat.com>, 01 Mar 2006
+ *
  * Still To Fix:
  * - Advisory locking is ignored here.
  * - Should use an own CAP_* category instead of CAP_SYS_ADMIN
@@ -74,6 +79,7 @@
 #include <linux/completion.h>
 #include <linux/highmem.h>
 #include <linux/gfp.h>
+#include <linux/mount.h>

 #include <asm/uaccess.h>

@@ -791,7 +797,8 @@ static int loop_set_fd(struct loop_devic
                 */
                if (!file->f_op->sendfile)
                        goto out_putf;
-               if (aops->prepare_write && aops->commit_write)
+               if (!(file->f_vfsmnt->mnt_sb->s_type->fs_flags & FS_AOPS_NEED_LOCKING) &&
+                       aops->prepare_write && aops->commit_write)
                        lo_flags |= LO_FLAGS_USE_AOPS;
                if (!(lo_flags & LO_FLAGS_USE_AOPS) && !file->f_op->write)
                        lo_flags |= LO_FLAGS_READ_ONLY;
diff -pur linux-2.6.16/include/linux/fs.h linux-2.6.16.patched/include/linux/fs.h
--- linux-2.6.16/include/linux/fs.h     2006-03-19 23:53:29.000000000 -0600
+++ linux-2.6.16.patched/include/linux/fs.h     2006-03-24 10:27:20.000000000 -0600
@@ -83,6 +83,7 @@ extern int dir_notify_enable;
 /* public flags for file_system_type */
 #define FS_REQUIRES_DEV 1
 #define FS_BINARY_MOUNTDATA 2
+#define FS_AOPS_NEED_LOCKING 4 /* Filesystem aops have special locking needs */
 #define FS_REVAL_DOT   16384   /* Check the paths ".", ".." for staleness */
 #define FS_ODD_RENAME  32768   /* Temporary stuff; will go away as soon
                                  * as nfs_rename() will be cleaned up