fuse: add support for SEEK_HOLE and SEEK_DATA in lseek

A useful performance improvement for accessing virtual machine images
via FUSE mount.

See https://bugzilla.redhat.com/show_bug.cgi?id=1220173 for a use-case
for glusterFS.

Signed-off-by: Ravishankar N <ravishankar@redhat.com>
Signed-off-by: Miklos Szeredi <miklos@szeredi.hu>

3 files changed, 84 insertions, 9 deletions

diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index 195476a24148..47f181191060 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -2231,20 +2231,77 @@ static sector_t fuse_bmap(struct address_space *mapping, sector_t block)
         return err ? 0 : outarg.block;
 }
 
+static loff_t fuse_lseek(struct file *file, loff_t offset, int whence)
+{
+        struct inode *inode = file->f_mapping->host;
+        struct fuse_conn *fc = get_fuse_conn(inode);
+        struct fuse_file *ff = file->private_data;
+        FUSE_ARGS(args);
+        struct fuse_lseek_in inarg = {
+                .fh = ff->fh,
+                .offset = offset,
+                .whence = whence
+        };
+        struct fuse_lseek_out outarg;
+        int err;
+
+        if (fc->no_lseek)
+                goto fallback;
+
+        args.in.h.opcode = FUSE_LSEEK;
+        args.in.h.nodeid = ff->nodeid;
+        args.in.numargs = 1;
+        args.in.args[0].size = sizeof(inarg);
+        args.in.args[0].value = &inarg;
+        args.out.numargs = 1;
+        args.out.args[0].size = sizeof(outarg);
+        args.out.args[0].value = &outarg;
+        err = fuse_simple_request(fc, &args);
+        if (err) {
+                if (err == -ENOSYS) {
+                        fc->no_lseek = 1;
+                        goto fallback;
+                }
+                return err;
+        }
+
+        return vfs_setpos(file, outarg.offset, inode->i_sb->s_maxbytes);
+
+fallback:
+        err = fuse_update_attributes(inode, NULL, file, NULL);
+        if (!err)
+                return generic_file_llseek(file, offset, whence);
+        else
+                return err;
+}
+
 static loff_t fuse_file_llseek(struct file *file, loff_t offset, int whence)
 {
         loff_t retval;
         struct inode *inode = file_inode(file);
 
-        /* No i_mutex protection necessary for SEEK_CUR and SEEK_SET */
-        if (whence == SEEK_CUR || whence == SEEK_SET)
-                return generic_file_llseek(file, offset, whence);
-
-        mutex_lock(&inode->i_mutex);
-        retval = fuse_update_attributes(inode, NULL, file, NULL);
-        if (!retval)
+        switch (whence) {
+        case SEEK_SET:
+        case SEEK_CUR:
+                 /* No i_mutex protection necessary for SEEK_CUR and SEEK_SET */
                 retval = generic_file_llseek(file, offset, whence);
-        mutex_unlock(&inode->i_mutex);
+                break;
+        case SEEK_END:
+                mutex_lock(&inode->i_mutex);
+                retval = fuse_update_attributes(inode, NULL, file, NULL);
+                if (!retval)
+                        retval = generic_file_llseek(file, offset, whence);
+                mutex_unlock(&inode->i_mutex);
+                break;
+        case SEEK_HOLE:
+        case SEEK_DATA:
+                mutex_lock(&inode->i_mutex);
+                retval = fuse_lseek(file, offset, whence);
+                mutex_unlock(&inode->i_mutex);
+                break;
+        default:
+                retval = -EINVAL;
+        }
 
         return retval;
 }
diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
index 405113101db8..ce394b5fe6b4 100644
--- a/fs/fuse/fuse_i.h
+++ b/fs/fuse/fuse_i.h
@@ -605,6 +605,9 @@ struct fuse_conn {
         /** Does the filesystem support asynchronous direct-IO submission? */
         unsigned async_dio:1;
 
+        /** Is lseek not implemented by fs? */
+        unsigned no_lseek:1;
+
         /** The number of requests waiting for completion */
         atomic_t num_waiting;
 
diff --git a/include/uapi/linux/fuse.h b/include/uapi/linux/fuse.h
index c9aca042e61d..5974fae54e12 100644
--- a/include/uapi/linux/fuse.h
+++ b/include/uapi/linux/fuse.h
@@ -102,6 +102,9 @@
  *  - add ctime and ctimensec to fuse_setattr_in
  *  - add FUSE_RENAME2 request
  *  - add FUSE_NO_OPEN_SUPPORT flag
+ *
+ *  7.24
+ *  - add FUSE_LSEEK for SEEK_HOLE and SEEK_DATA support
  */
 
 #ifndef _LINUX_FUSE_H
@@ -137,7 +140,7 @@
 #define FUSE_KERNEL_VERSION 7
 
 /** Minor version number of this interface */
-#define FUSE_KERNEL_MINOR_VERSION 23
+#define FUSE_KERNEL_MINOR_VERSION 24
 
 /** The node ID of the root inode */
 #define FUSE_ROOT_ID 1
@@ -358,6 +361,7 @@ enum fuse_opcode {
         FUSE_FALLOCATE     = 43,
         FUSE_READDIRPLUS   = 44,
         FUSE_RENAME2       = 45,
+        FUSE_LSEEK         = 46,
 
         /* CUSE specific operations */
         CUSE_INIT          = 4096,
@@ -758,4 +762,15 @@ struct fuse_notify_retrieve_in {
 /* Device ioctls: */
 #define FUSE_DEV_IOC_CLONE      _IOR(229, 0, uint32_t)
 
+struct fuse_lseek_in {
+        uint64_t        fh;
+        uint64_t        offset;
+        uint32_t        whence;
+        uint32_t        padding;
+};
+
+struct fuse_lseek_out {
+        uint64_t        offset;
+};
+
 #endif /* _LINUX_FUSE_H */