Merge lp:~gaul/percona-server/pwrite_partial_write into lp:percona-server/5.6

[Andrew Gaul]

[Laurynas Biveinis (laurynas-biveinis)]

Andrew -

Thanks for the patch. It is correct in general, I'm testing it with two additional changes:
- replace non-portable void* pointer arithmetics with an expression through casting to char*;
- the same bug is present in os_file_pread().

The same bug is present in os_file_pread()/os_file_pwrite() for systems that do not support pwrite()/pread(), e.g. Windows. We don't support any such platform, thus I am ignoring it for the now.

I'll attach the updated patch merge proposal to the bug report.

review: Needs Resubmitting

Unmerged revisions

519. By Andrew Gaul <email address hidden> on 2013-12-19

Handle partial writes in os0file.cc:os_file_pwrite

This could cause ibd files to contain bogus trailing zeros and non-page
size file sizes, which XtraBackup asserts on.

=== modified file 'Percona-Server/storage/innobase/os/os0file.cc'
--- Percona-Server/storage/innobase/os/os0file.cc	2013-12-05 17:23:10 +0000
+++ Percona-Server/storage/innobase/os/os0file.cc	2013-12-19 05:43:39 +0000
@@ -2624,12 +2624,13 @@
 	MONITOR_ATOMIC_INC(MONITOR_OS_PENDING_WRITES);
 #endif /* !HAVE_ATOMIC_BUILTINS || UNIV_WORD < 8 */
 
-	/* Handle signal interruptions correctly */
+	/* Handle partial writes and signal interruptions correctly */
 	for (ret = 0; ret < (ssize_t) n; ) {
-		n_written = pwrite(file, buf, (ssize_t)n, offs);
-		if (n_written > 0) {
+		n_written = pwrite(file, buf, ((ssize_t)n) - ret, offs);
+		if (n_written >= 0) {
 			ret += n_written;
 			offs += n_written;
+			buf += n_written;
 		} else if (n_written == -1 && errno == EINTR) {
 			continue;
 		} else {