fuse: add atomic open+truncate support

This patch allows fuse filesystems to implement open(..., O_TRUNC) as a single
request, instead of separate truncate and open requests.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

4 files changed, 13 insertions, 2 deletions

diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c
index 537d38bee13c..052327bd6c9d 100644
--- a/fs/fuse/dir.c
+++ b/fs/fuse/dir.c
@@ -1083,6 +1083,9 @@ static int fuse_do_setattr(struct dentry *entry, struct iattr *attr,
                         return err;
         }
 
+        if ((attr->ia_valid & ATTR_OPEN) && fc->atomic_o_trunc)
+                return 0;
+
         if (attr->ia_valid & ATTR_SIZE) {
                 unsigned long limit;
                 if (IS_SWAPFILE(inode))
diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index 4a28c3d37732..6726378661da 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -28,7 +28,9 @@ static int fuse_send_open(struct inode *inode, struct file *file, int isdir,
                 return PTR_ERR(req);
 
         memset(&inarg, 0, sizeof(inarg));
-        inarg.flags = file->f_flags & ~(O_CREAT | O_EXCL | O_NOCTTY | O_TRUNC);
+        inarg.flags = file->f_flags & ~(O_CREAT | O_EXCL | O_NOCTTY);
+        if (!fc->atomic_o_trunc)
+                inarg.flags &= ~O_TRUNC;
         req->in.h.opcode = isdir ? FUSE_OPENDIR : FUSE_OPEN;
         req->in.h.nodeid = get_node_id(inode);
         req->in.numargs = 1;
diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
index ffbcadaa7d67..b24fc9b386f8 100644
--- a/fs/fuse/fuse_i.h
+++ b/fs/fuse/fuse_i.h
@@ -320,6 +320,9 @@ struct fuse_conn {
         /** Do readpages asynchronously?  Only set in INIT */
         unsigned async_read : 1;
 
+        /** Do not send separate SETATTR request before open(O_TRUNC)  */
+        unsigned atomic_o_trunc : 1;
+
         /*
          * The following bitfields are only for optimization purposes
          * and hence races in setting them will not cause malfunction
diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
index 6ef3973f4048..3c13981f48e2 100644
--- a/fs/fuse/inode.c
+++ b/fs/fuse/inode.c
@@ -531,6 +531,8 @@ static void process_init_reply(struct fuse_conn *fc, struct fuse_req *req)
                                 fc->async_read = 1;
                         if (!(arg->flags & FUSE_POSIX_LOCKS))
                                 fc->no_lock = 1;
+                        if (arg->flags & FUSE_ATOMIC_O_TRUNC)
+                                fc->atomic_o_trunc = 1;
                 } else {
                         ra_pages = fc->max_read / PAGE_CACHE_SIZE;
                         fc->no_lock = 1;
@@ -553,7 +555,8 @@ static void fuse_send_init(struct fuse_conn *fc, struct fuse_req *req)
         arg->major = FUSE_KERNEL_VERSION;
         arg->minor = FUSE_KERNEL_MINOR_VERSION;
         arg->max_readahead = fc->bdi.ra_pages * PAGE_CACHE_SIZE;
-        arg->flags |= FUSE_ASYNC_READ | FUSE_POSIX_LOCKS | FUSE_FILE_OPS;
+        arg->flags |= FUSE_ASYNC_READ | FUSE_POSIX_LOCKS | FUSE_FILE_OPS |
+                FUSE_ATOMIC_O_TRUNC;
         req->in.h.opcode = FUSE_INIT;
         req->in.numargs = 1;
         req->in.args[0].size = sizeof(*arg);