9p: add locking to V9fsDir

If several threads concurrently call readdir() with the same directory
stream pointer, it is possible that they all get a pointer to the same
dirent structure, whose content is overwritten each time readdir() is
called.

We must thus serialize accesses to the dirent structure.

This may be achieved with a mutex like below:

lock_mutex();

readdir();

// work with the dirent

unlock_mutex();

This patch adds all the locking, to prepare the switch to readdir().

Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Greg Kurz <gkurz@linux.vnet.ibm.com>

1 files changed, 16 insertions, 0 deletions

diff --git a/hw/9pfs/9p.h b/hw/9pfs/9p.h
index 92ee309ef4..46d787627a 100644
--- a/hw/9pfs/9p.h
+++ b/hw/9pfs/9p.h
@@ -169,8 +169,24 @@ typedef struct V9fsXattr
 
 typedef struct V9fsDir {
     DIR *stream;
+    QemuMutex readdir_mutex;
 } V9fsDir;
 
+static inline void v9fs_readdir_lock(V9fsDir *dir)
+{
+    qemu_mutex_lock(&dir->readdir_mutex);
+}
+
+static inline void v9fs_readdir_unlock(V9fsDir *dir)
+{
+    qemu_mutex_unlock(&dir->readdir_mutex);
+}
+
+static inline void v9fs_readdir_init(V9fsDir *dir)
+{
+    qemu_mutex_init(&dir->readdir_mutex);
+}
+
 /*
  * Filled by fs driver on open and other
  * calls.