[RFC PATCH 6/6] block: Add a thread-pool version of fstat

[Fabiano Rosas <farosas@suse.de>]

From: João Silva <jsilva@suse.de>

The fstat call can take a long time to finish when running over
NFS. Add a version of it that runs in the thread pool.

Adapt one of its users, raw_co_get_allocated_file size to use the new
version. That function is called via QMP under the qemu_global_mutex
so it has a large chance of blocking VCPU threads in case it takes too
long to finish.

Signed-off-by: João Silva <jsilva@suse.de>
Signed-off-by: Fabiano Rosas <farosas@suse.de>
---
 block/file-posix.c      | 40 +++++++++++++++++++++++++++++++++++++---
 include/block/raw-aio.h |  4 +++-
 2 files changed, 40 insertions(+), 4 deletions(-)

diff --git a/block/file-posix.c b/block/file-posix.c
index 0ab158efba..0a29a6cc43 100644
--- a/block/file-posix.c
+++ b/block/file-posix.c
@@ -227,6 +227,9 @@ typedef struct RawPosixAIOData {
         struct {
             unsigned long op;
         } zone_mgmt;
+        struct {
+            struct stat *st;
+        } fstat;
     };
 } RawPosixAIOData;
 
@@ -2644,6 +2647,34 @@ static void raw_close(BlockDriverState *bs)
     }
 }
 
+static int handle_aiocb_fstat(void *opaque)
+{
+    RawPosixAIOData *aiocb = opaque;
+
+    if (fstat(aiocb->aio_fildes, aiocb->fstat.st) < 0) {
+        return -errno;
+    }
+
+    return 0;
+}
+
+static int coroutine_fn raw_co_fstat(BlockDriverState *bs, struct stat *st)
+{
+    BDRVRawState *s = bs->opaque;
+    RawPosixAIOData acb;
+
+    acb = (RawPosixAIOData) {
+        .bs             = bs,
+        .aio_fildes     = s->fd,
+        .aio_type       = QEMU_AIO_FSTAT,
+        .fstat          = {
+            .st = st,
+        },
+    };
+
+    return raw_thread_pool_submit(handle_aiocb_fstat, &acb);
+}
+
 /**
  * Truncates the given regular file @fd to @offset and, when growing, fills the
  * new space according to @prealloc.
@@ -2883,11 +2914,14 @@ static int64_t coroutine_fn raw_co_getlength(BlockDriverState *bs)
 static int64_t coroutine_fn raw_co_get_allocated_file_size(BlockDriverState *bs)
 {
     struct stat st;
-    BDRVRawState *s = bs->opaque;
+    int ret;
 
-    if (fstat(s->fd, &st) < 0) {
-        return -errno;
+    ret = raw_co_fstat(bs, &st);
+
+    if (ret) {
+        return ret;
     }
+
     return (int64_t)st.st_blocks * 512;
 }
 
diff --git a/include/block/raw-aio.h b/include/block/raw-aio.h
index 0fe85ade77..7dc6d24e21 100644
--- a/include/block/raw-aio.h
+++ b/include/block/raw-aio.h
@@ -31,6 +31,7 @@
 #define QEMU_AIO_ZONE_REPORT  0x0100
 #define QEMU_AIO_ZONE_MGMT    0x0200
 #define QEMU_AIO_ZONE_APPEND  0x0400
+#define QEMU_AIO_FSTAT        0x0800
 #define QEMU_AIO_TYPE_MASK \
         (QEMU_AIO_READ | \
          QEMU_AIO_WRITE | \
@@ -42,7 +43,8 @@
          QEMU_AIO_TRUNCATE | \
          QEMU_AIO_ZONE_REPORT | \
          QEMU_AIO_ZONE_MGMT | \
-         QEMU_AIO_ZONE_APPEND)
+         QEMU_AIO_ZONE_APPEND | \
+         QEMU_AIO_FSTAT)
 
 /* AIO flags */
 #define QEMU_AIO_MISALIGNED   0x1000
-- 
2.35.3