[PATCH] mm, fadvise: don't return -EINVAL when filesystem has no optimization way

[kosaki.motohiro@gmail.com]

From: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>

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

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

Current,input check of POSIX_FADV_WILLNEED has two problems.

1) require a_ops->readpage.
   But in fact, force_page_cache_readahead() only require
   a target filesystem has either ->readpage or ->readpages.
2) return -EINVAL when filesystem don't have ->readpage.
   But, posix says, it should be retrieved a hint. Thus fadvise()
   should return 0 if filesystem has no optimization way.
   Especially, userland application don't know a filesystem type
   of TMPDIR directory as Eric pointed out. Then, userland can't
   avoid this error. We shouldn't encourage to ignore syscall
   return value.

Thus, this patch change a return value to 0 when filesytem don't
support readahead.

Cc: linux-mm@kvack.org
Cc: Hugh Dickins <hughd@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Hillf Danton <dhillf@gmail.com>
Signed-off-by: Eric Wong <normalperson@yhbt.net>
Tested-by: Eric Wong <normalperson@yhbt.net>
Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
---
 mm/fadvise.c |   18 +++++++-----------
 1 files changed, 7 insertions(+), 11 deletions(-)

diff --git a/mm/fadvise.c b/mm/fadvise.c
index 469491e..33e6baf 100644
--- 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;
-- 
1.7.1

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