Commit 90330e68 authored Dec 18, 2015 by Abhi Das Committed by Al Viro Jan 09, 2016

fs: __generic_file_splice_read retry lookup on AOP_TRUNCATED_PAGE



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. This
behavior is now similar to do_generic_file_read().

Signed-off-by: Abhi Das <adas@redhat.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Cc: Bob Peterson <rpeterso@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

parent 0b2a6f23

fs/splice.c

+3 −5

Original line number	Diff line number	Diff line
		@@ -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;
		}

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