[PATCH v2] generic/465: just check the actual read data under dio read/write

[Xiao Yang <yangx.jy@cn.fujitsu.com>]

I got the following message when running generic/465 in ext4 data=journal mode
---------------------------------------------------------------
QA output created by 465
non-aio dio test
encounter an error: block 0 offset 4096, content 62
encounter an error: block 0 offset 122880, content 62
encounter an error: block 0 offset 274432, content 62
encounter an error: block 0 offset 86016, content 62
aio-dio test
encounter an error: block 0 offset 28672, content 62
encounter an error: block 0 offset 12288, content 62
encounter an error: block 2 offset 16384, content 62
encounter an error: block 1 offset 565248, content 62
---------------------------------------------------------------

In ext4 data=journal mode, direct read will fall back to buffer read, and buffer
read doesn't take inode lock, so it doesn't need to wait for the writer to finish
first and sees the intermediate inode size and returns data less than 1M.

We can just check the actual read data instead of the whole read buffer.

Signed-off-by: Xiao Yang <yangx.jy@cn.fujitsu.com>
---
 src/aio-dio-regress/aio-dio-append-write-read-race.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/src/aio-dio-regress/aio-dio-append-write-read-race.c b/src/aio-dio-regress/aio-dio-append-write-read-race.c
index 8f94d50..eaec784 100644
--- a/src/aio-dio-regress/aio-dio-append-write-read-race.c
+++ b/src/aio-dio-regress/aio-dio-append-write-read-race.c
@@ -43,6 +43,7 @@ struct io_data {
 	off_t offset;
 	char *buf;
 	int use_aio;
+	size_t act_sz;
 };
 
 int reader_ready = 0;
@@ -57,15 +58,14 @@ static void usage(const char *prog)
 static void *reader(void *arg)
 {
 	struct io_data *data = (struct io_data *)arg;
-	int ret;
 
 	memset(data->buf, 'b', data->blksize);
 	reader_ready = 1;
 	do {
-		ret = pread(data->fd, data->buf, data->blksize, data->offset);
-		if (ret < 0)
+		data->act_sz = pread(data->fd, data->buf, data->blksize, data->offset);
+		if (data->act_sz < 0)
 			perror("read file");
-	} while (ret <= 0);
+	} while (data->act_sz <= 0);
 
 	return NULL;
 }
@@ -203,7 +203,7 @@ int main(int argc, char *argv[])
 			goto err;
 		}
 
-		for (j = 0; j < blksize; j++) {
+		for (j = 0; j < rdata.act_sz; j++) {
 			if (rdata.buf[j] != 'a') {
 				fail("encounter an error: "
 					"block %d offset %d, content %x\n",
-- 
1.8.3.1