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mm, fadvise: don't return -EINVAL when filesystem cannot implement fa…

…dvise()

Eric Wong reported his test suite failex when /tmp is tmpfs.

https://lkml.org/lkml/2012/2/24/479

Currentlt the input check of POSIX_FADV_WILLNEED has two problems.

- requires a_ops->readpage.  But in fact, force_page_cache_readahead()
  requires that the target filesystem has either ->readpage or ->readpages.

- returns -EINVAL when the filesystem doesn't have ->readpage.  But
  posix says that fadvise is merely a hint.  Thus fadvise() should return
  0 if filesystem has no means of implementing fadvise().  The userland
  application should not know nor care whcih type of filesystem backs the
  TMPDIR directory, as Eric pointed out.  There is nothing which userspace
  can do to solve this error.

So change the return value to 0 when filesytem doesn't support readahead.

[akpm@linux-foundation.org: checkpatch fixes]
Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Hillf Danton <dhillf@gmail.com>
Signed-off-by: Eric Wong <normalperson@yhbt.net>
Tested-by: Eric Wong <normalperson@yhbt.net>
Reviewed-by: Wanlong Gao <gaowanlong@cn.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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1 parent c59e261 commit 3d3727cdb07ff17ddc3c551ef8d03d37b60a0372 @kosaki kosaki committed with Jul 31, 2012
Showing with 7 additions and 11 deletions.
  1. +7 −11 mm/fadvise.c
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@@ -93,11 +93,6 @@ SYSCALL_DEFINE(fadvise64_64)(int fd, loff_t offset, loff_t len, int advice)
spin_unlock(&file->f_lock);
break;
case POSIX_FADV_WILLNEED:
- if (!mapping->a_ops->readpage) {
- ret = -EINVAL;
- break;
- }
-
/* First and last PARTIAL page! */
start_index = offset >> PAGE_CACHE_SHIFT;
end_index = endbyte >> PAGE_CACHE_SHIFT;
@@ -106,12 +101,13 @@ SYSCALL_DEFINE(fadvise64_64)(int fd, loff_t offset, loff_t len, int advice)
nrpages = end_index - start_index + 1;
if (!nrpages)
nrpages = ~0UL;
-
- ret = force_page_cache_readahead(mapping, file,
- start_index,
- nrpages);
- if (ret > 0)
- ret = 0;
+
+ /*
+ * Ignore return value because fadvise() shall return
+ * success even if filesystem can't retrieve a hint,
+ */
+ force_page_cache_readahead(mapping, file, start_index,
+ nrpages);
break;
case POSIX_FADV_NOREUSE:
break;

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