Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1293310

[RFC v3 PATCH] fs: __generic_file_splice_read retry lookup on AOP_TRUNCATED_PAGE

Show all headers | View raw

During testing, I discovered that __generic_file_splice_read() returns
0 (EOF) when aops->readpage fails with AOP_TRUNCATED_PAGE on the first
page of a single/multi-page splice read operation. This EOF return code
causes the userspace test to (correctly) report a zero-length read error
when it was expecting otherwise.

The current strategy of returning a partial non-zero read when ->readpage
returns AOP_TRUNCATED_PAGE works only when the failed page is not the
first of the lot being processed.

This patch attempts to retry lookup and call ->readpage again on pages
that had previously failed with AOP_TRUNCATED_PAGE. With this patch, my
tests pass and I haven't noticed any unwanted side effects.

This version removes the thrice-retry loop and instead indefinitely
retries lookups on AOP_TRUNCATED_PAGE errors from ->readpage.

Signed-off-by: Abhi Das <adas@redhat.com>
Cc: Bob Peterson <rpeterso@redhat.com>
Cc: Jan Kara <jack@suse.com>
---
 fs/splice.c | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/fs/splice.c b/fs/splice.c
index 801c21c..277df71 100644
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -415,6 +415,7 @@ __generic_file_splice_read(struct file *in, loff_t *ppos,
 			 */
 			if (!page->mapping) {
 				unlock_page(page);
+retry_lookup:
 				page = find_or_create_page(mapping, index,
 						mapping_gfp_mask(mapping));
 
@@ -439,13 +440,10 @@ __generic_file_splice_read(struct file *in, loff_t *ppos,
 			error = mapping->a_ops->readpage(in, page);
 			if (unlikely(error)) {
 				/*
-				 * We really should re-lookup the page here,
-				 * but it complicates things a lot. Instead
-				 * lets just do what we already stored, and
-				 * we'll get it the next time we are called.
+				 * Re-lookup the page
 				 */
 				if (error == AOP_TRUNCATED_PAGE)
-					error = 0;
+					goto retry_lookup;
 
 				break;
 			}
-- 
2.4.3

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

Back to linux.kernel | Previous | Next — Next in thread | Find similar | Unroll thread

Thread

[RFC v3 PATCH] fs: __generic_file_splice_read retry lookup on AOP_TRUNCATED_PAGE Abhi Das <adas@redhat.com> - 2015-12-16 20:10 +0100
  Re: [RFC v3 PATCH] fs: __generic_file_splice_read retry lookup on  AOP_TRUNCATED_PAGE Jan Kara <jack@suse.cz> - 2015-12-17 20:30 +0100

csiph-web