hw/9pfs: make get_st_gen() return ENOTTY error on special files

Currently we silently ignore getversion requests for anything except
file or directory. Let's instead return ENOTTY error to indicate that
getversion is not supported. It makes implementation consistent on
all not-supported cases.
Signed-off-by: NKirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: NAneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>

hw/9pfs/virtio-9p-handle.c

@@ -591,7 +591,8 @@ static int handle_ioc_getversion(FsContext *ctx, V9fsPath *path,
      * We can get fd for regular files and directories only
      */
     if (!S_ISREG(st_mode) && !S_ISDIR(st_mode)) {
-            return 0;
+        errno = ENOTTY;
+        return -1;
     }
     err = handle_open(ctx, path, O_RDONLY, &fid_open);
     if (err < 0) {

hw/9pfs/virtio-9p-local.c

@@ -1077,7 +1077,8 @@ static int local_ioc_getversion(FsContext *ctx, V9fsPath *path,
      * We can get fd for regular files and directories only
      */
     if (!S_ISREG(st_mode) && !S_ISDIR(st_mode)) {
-            return 0;
+        errno = ENOTTY;
+        return -1;
     }
     err = local_open(ctx, path, O_RDONLY, &fid_open);
     if (err < 0) {

hw/9pfs/virtio-9p-proxy.c

@@ -1086,7 +1086,8 @@ static int proxy_ioc_getversion(FsContext *fs_ctx, V9fsPath *path,
      * we can get fd for regular files and directories only
      */
     if (!S_ISREG(st_mode) && !S_ISDIR(st_mode)) {
-        return 0;
+        errno = ENOTTY;
+        return -1;
     }
     err = v9fs_request(fs_ctx->private, T_GETVERSION, st_gen, "s", path);
     if (err < 0) {