fuse: Fix read for empty files.

Error handling for the guestfs_pread call was incorrect, which
meant that empty files could produce spurious error messages.

diff --git a/fuse/guestmount.c b/fuse/guestmount.c
index baf2b66..ba0d626 100644 (file)
--- a/fuse/guestmount.c
+++ b/fuse/guestmount.c
@@ -620,8 +620,14 @@ fg_read (const char *path, char *buf, size_t size, off_t offset,
   if (size > limit)
     size = limit;
 
   if (size > limit)
     size = limit;
 

+  /* Note the correct error handling here is tricky, because in the
+   * case where the call returns a zero-length buffer, it might return
+   * NULL.  However it won't adjust rsize along the error path, so we
+   * can set rsize to something beforehand and use that as a flag.
+   */
+  rsize = 1;

   r = guestfs_pread (g, path, size, offset, &rsize);
   r = guestfs_pread (g, path, size, offset, &rsize);

-  if (r == NULL)
+  if (rsize == 1 && r == NULL)

     return error ();
 
   /* This should never happen, but at least it stops us overflowing
     return error ();
 
   /* This should never happen, but at least it stops us overflowing