[PATCH] mm/readahead.c: need always return 0 when system call readahead() succeeds

[Chen Gang <gang.chen@asianux.com>]

For system call readahead(), need always return 0 instead of bytes read
when succeed. The related commit "fee53ce mm/readahead.c: return the
value which force_page_cache_readahead() returns" causes this issue.

This bug is found by LTP readahead02 test, the related output:

  [root@gchenlinux readahead]# ./readahead02
  readahead02    0  TINFO  :  creating test file of size: 67108864
  readahead02    0  TINFO  :  read_testfile(0)
  readahead02    0  TINFO  :  read_testfile(1)
  readahead02    1  TFAIL  :  unexpected failure - returned value = 16384, expected: 0
  readahead02    2  TPASS  :  offset is still at 0 as expected
  readahead02    0  TINFO  :  read_testfile(0) took: 2292819 usec
  readahead02    0  TINFO  :  read_testfile(1) took: 3524116 usec
  readahead02    0  TINFO  :  read_testfile(0) read: 67108864 bytes
  readahead02    0  TINFO  :  read_testfile(1) read: 0 bytes
  readahead02    3  TPASS  :  readahead saved some I/O
  readahead02    0  TINFO  :  cache can hold at least: 624316 kB
  readahead02    0  TINFO  :  read_testfile(0) used cache: 65476 kB
  readahead02    0  TINFO  :  read_testfile(1) used cache: 65632 kB
  readahead02    4  TPASS  :  using cache as expected

After this fix, it can pass LTP common test by readahead01 and readahead02.

  [root@gchenlinux readahead]# ./readahead01 
  readahead01    0  TINFO  :  test_bad_fd -1
  readahead01    1  TPASS  :  expected ret success - returned value = -1
  readahead01    2  TPASS  :  expected failure: TEST_ERRNO=EBADF(9): Bad file descriptor
  readahead01    0  TINFO  :  test_bad_fd O_WRONLY
  readahead01    3  TPASS  :  expected ret success - returned value = -1
  readahead01    4  TPASS  :  expected failure: TEST_ERRNO=EBADF(9): Bad file descriptor
  readahead01    0  TINFO  :  test_invalid_fd pipe
  readahead01    5  TPASS  :  expected ret success - returned value = -1
  readahead01    6  TPASS  :  expected failure: TEST_ERRNO=EINVAL(22): Invalid argument
  readahead01    0  TINFO  :  test_invalid_fd socket
  readahead01    7  TPASS  :  expected ret success - returned value = -1
  readahead01    8  TPASS  :  expected failure: TEST_ERRNO=EINVAL(22): Invalid argument
  [root@gchenlinux readahead]# ./readahead02
  readahead02    0  TINFO  :  creating test file of size: 67108864
  readahead02    0  TINFO  :  read_testfile(0)
  readahead02    0  TINFO  :  read_testfile(1)
  readahead02    1  TPASS  :  expected ret success - returned value = 0
  readahead02    2  TPASS  :  offset is still at 0 as expected
  readahead02    0  TINFO  :  read_testfile(0) took: 3327468 usec
  readahead02    0  TINFO  :  read_testfile(1) took: 2802184 usec
  readahead02    0  TINFO  :  read_testfile(0) read: 67108864 bytes
  readahead02    0  TINFO  :  read_testfile(1) read: 0 bytes
  readahead02    3  TPASS  :  readahead saved some I/O
  readahead02    0  TINFO  :  cache can hold at least: 794800 kB
  readahead02    0  TINFO  :  read_testfile(0) used cache: 66704 kB
  readahead02    0  TINFO  :  read_testfile(1) used cache: 65528 kB
  readahead02    4  TPASS  :  using cache as expected


Signed-off-by: Chen Gang <gang.chen@asianux.com>
---
 mm/readahead.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/mm/readahead.c b/mm/readahead.c
index 1eee42b..83a202e 100644
--- a/mm/readahead.c
+++ b/mm/readahead.c
@@ -592,5 +592,5 @@ SYSCALL_DEFINE3(readahead, int, fd, loff_t, offset, size_t, count)
 		}
 		fdput(f);
 	}
-	return ret;
+	return ret < 0 ? ret : 0;
 }
-- 
1.7.7.6

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