On Fri, 24 Sep 2010 14:24:31 -0500 Steve French <smfrench@xxxxxxxxx> wrote: > On Fri, Sep 24, 2010 at 2:08 PM, Jeff Layton <jlayton@xxxxxxxxxx> wrote: > > On Fri, 24 Sep 2010 13:43:40 -0500 > > Steve French <smfrench@xxxxxxxxx> wrote: > > > >> It don't think it is a correctness issue - if close wants to do an > >> fsync why do we have a flush routine at all? close is the only place > >> flush is called. This seems very wrong to require additional > >> semantics beyond Unix semantics here (and slows close performance way > >> down unnecessarily). Even if we go async we would initiate i/o on > >> these before we return close to the user - and we are not going to > >> close the network handle of course until all network writes complete. > >> > >> At a minimum, we don't need to do an fsync (flush with wait) on close > >> if there is more than one handle to that inode open - and should be > >> able to just do flush > >> > > > > What does this have to do with fsync? The flush operation is to flush > > out data to the server prior to close. CIFS is not like a local fs or > > even NFS. We have to have an open filehandle in order to write out > > data. > > fsync is an fs file operation, handle based - so why do we need a distinct > flush call if it has identical semantics? > > fsync has much more strict semantics than close. For many local filesystems that implies a barrier or something equivalent to ensure that it actually made it to the media. For the CIFS case, we also issue a SMB_COM_FLUSH in the fsync case, but not for close. flush is for the close(2) call. Not all filesystems need to flush data to disk on close. A local filesystem may be perfectly able to keep the data in pagecache and write it out whenever it gets to it even long after all file descriptors are closed. CIFS is not like that -- no filehandle == no writeback. Thus, we need to wait for writeback to complete before allowing writable filehandles to be closed. -- Jeff Layton <jlayton@xxxxxxxxxx> -- To unsubscribe from this list: send the line "unsubscribe linux-cifs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
