svn commit: r253050 - head/sys/fs/ext2fs

[Bruce Evans]

On Tue, 9 Jul 2013, Pedro F. Giffuni wrote:

> Author: pfg
> Date: Tue Jul  9 01:31:04 2013
> New Revision: 253050
> URL: http://svnweb.freebsd.org/changeset/base/253050
>
> Log:
>  Enhancement when writing an entire block of a file.
>
>  Merge from UFS r231313:
>
>  This change first attempts the uiomove() to the newly allocated
>  (and dirty) buffer and only zeros it if the uiomove() fails. The
>  effect is to eliminate the gratuitous zeroing of the buffer in
>  the usual case where the uiomove() successfully fills it.
>
>  MFC after:	3 days
>
> Modified:
>  head/sys/fs/ext2fs/ext2_vnops.c
>
> Modified: head/sys/fs/ext2fs/ext2_vnops.c
> ==============================================================================
> --- head/sys/fs/ext2fs/ext2_vnops.c	Tue Jul  9 01:05:28 2013	(r253049)
> +++ head/sys/fs/ext2fs/ext2_vnops.c	Tue Jul  9 01:31:04 2013	(r253050)
> @@ -1812,15 +1812,6 @@ ext2_write(struct vop_write_args *ap)
> 		if (error != 0)
> 			break;
>
> -		/*
> -		 * If the buffer is not valid and we did not clear garbage
> -		 * out above, we have to do so here even though the write
> -		 * covers the entire buffer in order to avoid a mmap()/write
> -		 * race where another process may see the garbage prior to
> -		 * the uiomove() for a write replacing it.
> -		 */
> -		if ((bp->b_flags & B_CACHE) == 0 && fs->e2fs_bsize <= xfersize)
> -			vfs_bio_clrbuf(bp);
> 		if ((ioflag & (IO_SYNC|IO_INVAL)) == (IO_SYNC|IO_INVAL))
> 			bp->b_flags |= B_NOCACHE;
> 		if (uio->uio_offset + xfersize > ip->i_size)
> @@ -1831,6 +1822,26 @@ ext2_write(struct vop_write_args *ap)
>
> 		error =
> 		    uiomove((char *)bp->b_data + blkoffset, (int)xfersize, uio);
> +		/*
> +		 * If the buffer is not already filled and we encounter an
> +		 * error while trying to fill it, we have to clear out any
> +		 * garbage data from the pages instantiated for the buffer.
> +		 * If we do not, a failed uiomove() during a write can leave
> +		 * the prior contents of the pages exposed to a userland mmap.
> +		 *
> +		 * Note that we need only clear buffers with a transfer size
> +		 * equal to the block size because buffers with a shorter
> +		 * transfer size were cleared above by the call to ext2_balloc()
> +		 * with the BA_CLRBUF flag set.
> +		 *
> +		 * If the source region for uiomove identically mmaps the
> +		 * buffer, uiomove() performed the NOP copy, and the buffer
> +		 * content remains valid because the page fault handler
> +		 * validated the pages.
> +		 */
> +		if (error != 0 && (bp->b_flags & B_CACHE) == 0 &&
> +		    fs->e2fs_bsize == xfersize)
> +			vfs_bio_clrbuf(bp);
> 		if (ioflag & (IO_VMIO|IO_DIRECT)) {
> 			bp->b_flags |= B_RELBUF;
> 		}
>