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 fixes a return code issue pointed out by Bob Peterson.
Signed-off-by: Abhi Das <a...@redhat.com>
Cc: Bob Peterson <rpete...@redhat.com>
---
fs/splice.c | 13 +++++++------
1 file changed, 7 insertions(+), 6 deletions(-)
diff --git a/fs/splice.c b/fs/splice.c
index 801c21c..365cd2a 100644
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -387,6 +387,7 @@ __generic_file_splice_read(struct file *in, loff_t *ppos,
spd.nr_pages = 0;
for (page_nr = 0; page_nr < nr_pages; page_nr++) {
unsigned int this_len;
+ int retries = 0;
if (!len)
break;
@@ -415,6 +416,7 @@ __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));
@@ -439,14 +441,13 @@ __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)
+ if (error == AOP_TRUNCATED_PAGE) {
error = 0;
-
+ if (retries++ < 3)
+ goto retry_lookup;
+ }
break;
}
}
--
2.4.3
--
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