[PULL 6/7] 9pfs: differentiate readdir lock between 9P2000.u vs. 9P2000.L

[Christian Schoenebeck <qemu_oss@crudebyte.com>]

Previous patch suggests that it might make sense to use a different mutex
type now while handling readdir requests, depending on the precise
protocol variant, as v9fs_do_readdir_with_stat() (used by 9P2000.u) uses
a CoMutex to avoid deadlocks that might happen with QemuMutex otherwise,
whereas do_readdir_many() (used by 9P2000.L) should better use a
QemuMutex, as the precise behaviour of a failed CoMutex lock on fs driver
side would not be clear.

And to avoid the wrong lock type being used, be now strict and error out
if a 9P2000.L client sends a Tread on a directory, and likeweise error out
if a 9P2000.u client sends a Treaddir request.

This patch is just intended as transitional measure, as currently 9P2000.u
vs. 9P2000.L implementations currently differ where the main logic of
fetching directory entries is located at (9P2000.u still being more top
half focused, while 9P2000.L already being bottom half focused in regards
to fetching directory entries that is).

Signed-off-by: Christian Schoenebeck <qemu_oss@crudebyte.com>
Message-Id: <9a2ddc347e533b0d801866afd9dfac853d2d4106.1596012787.git.qemu_oss@crudebyte.com>
Signed-off-by: Christian Schoenebeck <qemu_oss@crudebyte.com>
---
 hw/9pfs/9p.c | 21 ++++++++++++++++++---
 hw/9pfs/9p.h | 27 ++++++++++++++++++++++-----
 2 files changed, 40 insertions(+), 8 deletions(-)

diff --git a/hw/9pfs/9p.c b/hw/9pfs/9p.c
index cc4094b971..7bb994bbf2 100644
--- a/hw/9pfs/9p.c
+++ b/hw/9pfs/9p.c
@@ -314,8 +314,8 @@ static V9fsFidState *alloc_fid(V9fsState *s, int32_t fid)
     f->next = s->fid_list;
     s->fid_list = f;
 
-    v9fs_readdir_init(&f->fs.dir);
-    v9fs_readdir_init(&f->fs_reclaim.dir);
+    v9fs_readdir_init(s->proto_version, &f->fs.dir);
+    v9fs_readdir_init(s->proto_version, &f->fs_reclaim.dir);
 
     return f;
 }
@@ -2228,7 +2228,14 @@ static void coroutine_fn v9fs_read(void *opaque)
         goto out_nofid;
     }
     if (fidp->fid_type == P9_FID_DIR) {
-
+        if (s->proto_version != V9FS_PROTO_2000U) {
+            warn_report_once(
+                "9p: bad client: T_read request on directory only expected "
+                "with 9P2000.u protocol version"
+            );
+            err = -EOPNOTSUPP;
+            goto out;
+        }
         if (off == 0) {
             v9fs_co_rewinddir(pdu, fidp);
         }
@@ -2446,6 +2453,14 @@ static void coroutine_fn v9fs_readdir(void *opaque)
         retval = -EINVAL;
         goto out;
     }
+    if (s->proto_version != V9FS_PROTO_2000L) {
+        warn_report_once(
+            "9p: bad client: T_readdir request only expected with 9P2000.L "
+            "protocol version"
+        );
+        retval = -EOPNOTSUPP;
+        goto out;
+    }
     count = v9fs_do_readdir(pdu, fidp, (off_t) initial_offset, max_count);
     if (count < 0) {
         retval = count;
diff --git a/hw/9pfs/9p.h b/hw/9pfs/9p.h
index 93b7030edf..3dd1b50b1a 100644
--- a/hw/9pfs/9p.h
+++ b/hw/9pfs/9p.h
@@ -197,22 +197,39 @@ typedef struct V9fsXattr
 
 typedef struct V9fsDir {
     DIR *stream;
-    CoMutex readdir_mutex;
+    P9ProtoVersion proto_version;
+    /* readdir mutex type used for 9P2000.u protocol variant */
+    CoMutex readdir_mutex_u;
+    /* readdir mutex type used for 9P2000.L protocol variant */
+    QemuMutex readdir_mutex_L;
 } V9fsDir;
 
 static inline void v9fs_readdir_lock(V9fsDir *dir)
 {
-    qemu_co_mutex_lock(&dir->readdir_mutex);
+    if (dir->proto_version == V9FS_PROTO_2000U) {
+        qemu_co_mutex_lock(&dir->readdir_mutex_u);
+    } else {
+        qemu_mutex_lock(&dir->readdir_mutex_L);
+    }
 }
 
 static inline void v9fs_readdir_unlock(V9fsDir *dir)
 {
-    qemu_co_mutex_unlock(&dir->readdir_mutex);
+    if (dir->proto_version == V9FS_PROTO_2000U) {
+        qemu_co_mutex_unlock(&dir->readdir_mutex_u);
+    } else {
+        qemu_mutex_unlock(&dir->readdir_mutex_L);
+    }
 }
 
-static inline void v9fs_readdir_init(V9fsDir *dir)
+static inline void v9fs_readdir_init(P9ProtoVersion proto_version, V9fsDir *dir)
 {
-    qemu_co_mutex_init(&dir->readdir_mutex);
+    dir->proto_version = proto_version;
+    if (proto_version == V9FS_PROTO_2000U) {
+        qemu_co_mutex_init(&dir->readdir_mutex_u);
+    } else {
+        qemu_mutex_init(&dir->readdir_mutex_L);
+    }
 }
 
 /**
-- 
2.20.1