mm, fadvise: don't return -EINVAL when filesystem cannot implement fadvise()

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.

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>

diff --git a/mm/fadvise.c b/mm/fadvise.c
index 469491e0af79fed994d48fd4ada817f8e50c6d6a..33e6baff72fe89723bb0ddbeaf934e6848061d7b 100644 (file)
--- a/mm/fadvise.c
+++ b/mm/fadvise.c
@@ -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;