[PATCH v3] mm: readahead: check return value which force_page_cache_readahead() returns

[Chen Gang <gang.chen@xxxxxxxxxxx>]

force_page_cache_readahead() may fail, so the callers who want to know
about it need check the return value.

force_page_cache_readahead() need not return actual read length, since
no callers care about it, and which may lead callers misunderstanding:
treat non-zero as failure.

And now, 2 callers need not check the return value:

 - in fadvise64_64(), it contents the related comment near above.
   (return success even if filesystem can't retrieve a hint).

 - page_cache_sync_readahead() itself need not return value
   (only can not improve performance when it fails).


Signed-off-by: Chen Gang <gang.chen@xxxxxxxxxxx>
---
 mm/madvise.c   |    4 ++--
 mm/readahead.c |   11 +++--------
 2 files changed, 5 insertions(+), 10 deletions(-)

diff --git a/mm/madvise.c b/mm/madvise.c
index 539eeb9..dee8d46 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -247,8 +247,8 @@ static long madvise_willneed(struct vm_area_struct *vma,
 		end = vma->vm_end;
 	end = ((end - vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff;
 
-	force_page_cache_readahead(file->f_mapping, file, start, end - start);
-	return 0;
+	return force_page_cache_readahead(file->f_mapping, file,
+					start, end - start);
 }
 
 /*
diff --git a/mm/readahead.c b/mm/readahead.c
index 7cdbb44..b186d93 100644
--- a/mm/readahead.c
+++ b/mm/readahead.c
@@ -211,8 +211,6 @@ out:
 int force_page_cache_readahead(struct address_space *mapping, struct file *filp,
 		pgoff_t offset, unsigned long nr_to_read)
 {
-	int ret = 0;
-
 	if (unlikely(!mapping->a_ops->readpage && !mapping->a_ops->readpages))
 		return -EINVAL;
 
@@ -227,14 +225,12 @@ int force_page_cache_readahead(struct address_space *mapping, struct file *filp,
 		err = __do_page_cache_readahead(mapping, filp,
 						offset, this_chunk, 0);
 		if (err < 0) {
-			ret = err;
-			break;
+			return err;
 		}
-		ret += err;
 		offset += this_chunk;
 		nr_to_read -= this_chunk;
 	}
-	return ret;
+	return 0;
 }
 
 /*
@@ -576,8 +572,7 @@ do_readahead(struct address_space *mapping, struct file *filp,
 	if (!mapping || !mapping->a_ops)
 		return -EINVAL;
 
-	force_page_cache_readahead(mapping, filp, index, nr);
-	return 0;
+	return force_page_cache_readahead(mapping, filp, index, nr);
 }
 
 SYSCALL_DEFINE3(readahead, int, fd, loff_t, offset, size_t, count)
-- 
1.7.7.6

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