9pfs: add new function v9fs_co_readdir_many()

The newly added function v9fs_co_readdir_many() retrieves multiple
directory entries with a single fs driver request. It is intended to
replace uses of v9fs_co_readdir(), the latter only retrieves a
single directory entry per fs driver request instead.

The reason for this planned replacement is that for every fs driver
request the coroutine is dispatched from main I/O thread to a
background I/O thread and eventually dispatched back to main I/O
thread. Hopping between threads adds latency. So if a 9pfs Treaddir
request reads a large amount of directory entries, this currently
sums up to huge latencies of several hundred ms or even more. So
using v9fs_co_readdir_many() instead of v9fs_co_readdir() will
provide significant performance improvements.

Signed-off-by: Christian Schoenebeck <qemu_oss@crudebyte.com>
Message-Id: <73dc827a12ef577ae7e644dcf34a5c0e443ab42f.1596012787.git.qemu_oss@crudebyte.com>
Signed-off-by: Christian Schoenebeck <qemu_oss@crudebyte.com>

1 files changed, 3 insertions, 0 deletions

diff --git a/hw/9pfs/coth.h b/hw/9pfs/coth.h
index c2cdc7a9ea..fd4a45bc7c 100644
--- a/hw/9pfs/coth.h
+++ b/hw/9pfs/coth.h
@@ -49,6 +49,9 @@
 void co_run_in_worker_bh(void *);
 int coroutine_fn v9fs_co_readlink(V9fsPDU *, V9fsPath *, V9fsString *);
 int coroutine_fn v9fs_co_readdir(V9fsPDU *, V9fsFidState *, struct dirent **);
+int coroutine_fn v9fs_co_readdir_many(V9fsPDU *, V9fsFidState *,
+                                      struct V9fsDirEnt **, off_t, int32_t,
+                                      bool);
 off_t coroutine_fn v9fs_co_telldir(V9fsPDU *, V9fsFidState *);
 void coroutine_fn v9fs_co_seekdir(V9fsPDU *, V9fsFidState *, off_t);
 void coroutine_fn v9fs_co_rewinddir(V9fsPDU *, V9fsFidState *);