[Qemu-devel] [PATCH 28/29] posix-aio-compat: Allow read after EOF

[Kevin Wolf <kwolf@redhat.com>]

In order to be able to transparently replace bdrv_read calls by bdrv_co_read,
reading beyond EOF must produce zeros instead of short reads for AIO, too.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
---
 posix-aio-compat.c |   19 +++++++++++++++++++
 1 files changed, 19 insertions(+), 0 deletions(-)

diff --git a/posix-aio-compat.c b/posix-aio-compat.c
index 788d113..8dc00cb 100644
--- a/posix-aio-compat.c
+++ b/posix-aio-compat.c
@@ -198,6 +198,12 @@ static ssize_t handle_aiocb_rw_vector(struct qemu_paiocb *aiocb)
     return len;
 }
 
+/*
+ * Read/writes the data to/from a given linear buffer.
+ *
+ * Returns the number of bytes handles or -errno in case of an error. Short
+ * reads are only returned if the end of the file is reached.
+ */
 static ssize_t handle_aiocb_rw_linear(struct qemu_paiocb *aiocb, char *buf)
 {
     ssize_t offset = 0;
@@ -334,6 +340,19 @@ static void *aio_thread(void *unused)
 
         switch (aiocb->aio_type & QEMU_AIO_TYPE_MASK) {
         case QEMU_AIO_READ:
+            ret = handle_aiocb_rw(aiocb);
+            if (ret >= 0 && ret < aiocb->aio_nbytes && aiocb->common.bs->growable) {
+                /* A short read means that we have reached EOF. Pad the buffer
+                 * with zeros for bytes after EOF. */
+                QEMUIOVector qiov;
+
+                qemu_iovec_init_external(&qiov, aiocb->aio_iov,
+                                         aiocb->aio_niov);
+                qemu_iovec_memset_skip(&qiov, 0, aiocb->aio_nbytes - ret, ret);
+
+                ret = aiocb->aio_nbytes;
+            }
+            break;
         case QEMU_AIO_WRITE:
             ret = handle_aiocb_rw(aiocb);
             break;
-- 
1.7.6