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Date:      Tue, 21 Feb 2012 01:43:31 +0000 (UTC)
From:      Konstantin Belousov <kib@FreeBSD.org>
To:        src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-stable@freebsd.org, svn-src-stable-9@freebsd.org
Subject:   svn commit: r231953 - stable/9/sys/ufs/ffs
Message-ID:  <201202210143.q1L1hV6K076765@svn.freebsd.org>

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Author: kib
Date: Tue Feb 21 01:43:31 2012
New Revision: 231953
URL: http://svn.freebsd.org/changeset/base/231953

Log:
  MFC r231313 (by mckusick):
  First attempt 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.

Modified:
  stable/9/sys/ufs/ffs/ffs_vnops.c
Directory Properties:
  stable/9/sys/   (props changed)

Modified: stable/9/sys/ufs/ffs/ffs_vnops.c
==============================================================================
--- stable/9/sys/ufs/ffs/ffs_vnops.c	Tue Feb 21 01:37:27 2012	(r231952)
+++ stable/9/sys/ufs/ffs/ffs_vnops.c	Tue Feb 21 01:43:31 2012	(r231953)
@@ -718,15 +718,6 @@ ffs_write(ap)
 			vnode_pager_setsize(vp, ip->i_size);
 			break;
 		}
-		/*
-		 * If the buffer is not valid 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().  XXX deal with uiomove() errors a better way.
-		 */
-		if ((bp->b_flags & B_CACHE) == 0 && fs->fs_bsize <= xfersize)
-			vfs_bio_clrbuf(bp);
 		if (ioflag & IO_DIRECT)
 			bp->b_flags |= B_DIRECT;
 		if ((ioflag & (IO_SYNC|IO_INVAL)) == (IO_SYNC|IO_INVAL))
@@ -743,6 +734,26 @@ ffs_write(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 UFS_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->fs_bsize == xfersize)
+			vfs_bio_clrbuf(bp);
 		if ((ioflag & (IO_VMIO|IO_DIRECT)) &&
 		   (LIST_EMPTY(&bp->b_dep))) {
 			bp->b_flags |= B_RELBUF;



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