Short reads/writes can happen. One way to reproduce them is via our
FUSE export, with the following diff applied (%s/escaped // to apply --
if you put plain diffs in commit messages, git-am will apply them, and I
would rather avoid breaking FUSE accidentally via this patch):
escaped diff --git a/block/export/fuse.c b/block/export/fuse.c
escaped index a2a478d293..67dc50a412 100644
escaped --- a/block/export/fuse.c
escaped +++ b/block/export/fuse.c
@@ -828,7 +828,7 @@ static ssize_t coroutine_fn GRAPH_RDLOCK
fuse_co_init(FuseExport *exp, struct fuse_init_out *out,
const struct fuse_init_in_compat *in)
{
- const uint32_t supported_flags = FUSE_ASYNC_READ | FUSE_ASYNC_DIO;
+ const uint32_t supported_flags = FUSE_ASYNC_READ;
if (in->major != 7) {
error_report("FUSE major version mismatch: We have 7, but kernel has
%"
@@ -1060,6 +1060,8 @@ fuse_co_read(FuseExport *exp, void **bufptr, uint64_t
offset, uint32_t size)
void *buf;
int ret;
+ size = MIN(size, 4096);
+
/* Limited by max_read, should not happen */
if (size > FUSE_MAX_READ_BYTES) {
return -EINVAL;
@@ -1110,6 +1112,8 @@ fuse_co_write(FuseExport *exp, struct fuse_write_out *out,
int64_t blk_len;
int ret;
+ size = MIN(size, 4096);
+
QEMU_BUILD_BUG_ON(FUSE_MAX_WRITE_BYTES > BDRV_REQUEST_MAX_BYTES);
/* Limited by max_write, should not happen */
if (size > FUSE_MAX_WRITE_BYTES) {
Then:
$ ./qemu-img create -f raw test.raw 8k
Formatting 'test.raw', fmt=raw size=8192
$ ./qemu-io -f raw -c 'write -P 42 0 8k' test.raw
wrote 8192/8192 bytes at offset 0
8 KiB, 1 ops; 00.00 sec (64.804 MiB/sec and 8294.9003 ops/sec)
$ hexdump -C test.raw
00000000 2a 2a 2a 2a 2a 2a 2a 2a 2a 2a 2a 2a 2a 2a 2a 2a |****************|
*
00002000
With aio=threads, short I/O works:
$ storage-daemon/qemu-storage-daemon \
--blockdev file,node-name=test,filename=test.raw \
--export fuse,id=exp,node-name=test,mountpoint=test.raw,writable=true
Other shell:
$ ./qemu-io --image-opts -c 'read -P 42 0 8k' \
driver=file,filename=test.raw,cache.direct=on,aio=threads
read 8192/8192 bytes at offset 0
8 KiB, 1 ops; 00.00 sec (36.563 MiB/sec and 4680.0923 ops/sec)
$ ./qemu-io --image-opts -c 'write -P 23 0 8k' \
driver=file,filename=test.raw,cache.direct=on,aio=threads
wrote 8192/8192 bytes at offset 0
8 KiB, 1 ops; 00.00 sec (35.995 MiB/sec and 4607.2970 ops/sec)
$ hexdump -C test.raw
00000000 17 17 17 17 17 17 17 17 17 17 17 17 17 17 17 17 |................|
*
00002000
But with aio=native, it does not:
$ ./qemu-io --image-opts -c 'read -P 23 0 8k' \
driver=file,filename=test.raw,cache.direct=on,aio=native
Pattern verification failed at offset 0, 8192 bytes
read 8192/8192 bytes at offset 0
8 KiB, 1 ops; 00.00 sec (86.155 MiB/sec and 11027.7900 ops/sec)
$ ./qemu-io --image-opts -c 'write -P 42 0 8k' \
driver=file,filename=test.raw,cache.direct=on,aio=native
write failed: No space left on device
$ hexdump -C test.raw
00000000 2a 2a 2a 2a 2a 2a 2a 2a 2a 2a 2a 2a 2a 2a 2a 2a |****************|
*
00001000 17 17 17 17 17 17 17 17 17 17 17 17 17 17 17 17 |................|
*
00002000
This patch fixes that.
Signed-off-by: Hanna Czenczek <[email protected]>
---
block/linux-aio.c | 61 ++++++++++++++++++++++++++++++++++++++++-------
1 file changed, 53 insertions(+), 8 deletions(-)
diff --git a/block/linux-aio.c b/block/linux-aio.c
index 1f25339dc9..01621d4794 100644
--- a/block/linux-aio.c
+++ b/block/linux-aio.c
@@ -46,6 +46,10 @@ struct qemu_laiocb {
size_t nbytes;
QEMUIOVector *qiov;
+ /* For handling short reads/writes */
+ size_t total_done;
+ QEMUIOVector resubmit_qiov;
+
int type;
BdrvRequestFlags flags;
uint64_t dev_max_batch;
@@ -73,28 +77,61 @@ struct LinuxAioState {
};
static void ioq_submit(LinuxAioState *s);
+static int laio_do_submit(struct qemu_laiocb *laiocb);
static inline ssize_t io_event_ret(struct io_event *ev)
{
return (ssize_t)(((uint64_t)ev->res2 << 32) | ev->res);
}
+/**
+ * Retry tail of short requests.
+ */
+static int laio_resubmit_short_io(struct qemu_laiocb *laiocb, size_t done)
+{
+ QEMUIOVector *resubmit_qiov = &laiocb->resubmit_qiov;
+
+ laiocb->total_done += done;
+
+ if (!resubmit_qiov->iov) {
+ qemu_iovec_init(resubmit_qiov, laiocb->qiov->niov);
+ } else {
+ qemu_iovec_reset(resubmit_qiov);
+ }
+ qemu_iovec_concat(resubmit_qiov, laiocb->qiov,
+ laiocb->total_done, laiocb->nbytes - laiocb->total_done);
+
+ return laio_do_submit(laiocb);
+}
+
/*
* Completes an AIO request.
*/
static void qemu_laio_process_completion(struct qemu_laiocb *laiocb)
{
- int ret;
+ ssize_t ret;
ret = laiocb->ret;
if (ret != -ECANCELED) {
- if (ret == laiocb->nbytes) {
+ if (ret == laiocb->nbytes - laiocb->total_done) {
ret = 0;
+ } else if (ret > 0 && (laiocb->type == QEMU_AIO_READ ||
+ laiocb->type == QEMU_AIO_WRITE)) {
+ ret = laio_resubmit_short_io(laiocb, ret);
+ if (!ret) {
+ return;
+ }
} else if (ret >= 0) {
- /* Short reads mean EOF, pad with zeros. */
+ /*
+ * For normal reads and writes, we only get here if ret == 0, which
+ * means EOF for reads and ENOSPC for writes.
+ * For zone-append, we get here with any ret >= 0, which we just
+ * treat as ENOSPC, too (safer than resubmitting, probably, but not
+ * 100 % clear).
+ */
if (laiocb->type == QEMU_AIO_READ) {
- qemu_iovec_memset(laiocb->qiov, ret, 0,
- laiocb->qiov->size - ret);
+ qemu_iovec_memset(laiocb->qiov, laiocb->total_done, 0,
+ laiocb->qiov->size - laiocb->total_done);
} else {
ret = -ENOSPC;
}
@@ -102,6 +139,7 @@ static void qemu_laio_process_completion(struct qemu_laiocb
*laiocb)
}
laiocb->ret = ret;
+ qemu_iovec_destroy(&laiocb->resubmit_qiov);
