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From: Peter Wemm <peter@FreeBSD.org>
Date: Tue, 3 May 2016 00:09:13 +0000 (UTC)
To: src-committers@freebsd.org, svn-src-all@freebsd.org,
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Subject: svn commit: r298949 - head/sys/boot/i386/zfsboot
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Author: peter
Date: Tue May  3 00:09:13 2016
New Revision: 298949
URL: https://svnweb.freebsd.org/changeset/base/298949

Log:
  Change a rounding operation that had missing braces into a roundup2()
  macro.  Adjust the buffer clipping code to work as expected.
  
  This prevented a number of machines in the FreeBSD.org cluster from
  booting due to "ZFS: i/o error - all block copies unavailable"
  after an unclean shutdown.

Modified:
  head/sys/boot/i386/zfsboot/zfsboot.c

Modified: head/sys/boot/i386/zfsboot/zfsboot.c
==============================================================================
--- head/sys/boot/i386/zfsboot/zfsboot.c	Mon May  2 22:58:11 2016	(r298948)
+++ head/sys/boot/i386/zfsboot/zfsboot.c	Tue May  3 00:09:13 2016	(r298949)
@@ -224,21 +224,18 @@ vdev_read(vdev_t *vdev, void *priv, off_
 
 	while (bytes > 0) {
 		nb = bytes / DEV_BSIZE;
-		if (nb > READ_BUF_SIZE / DEV_BSIZE)
-			nb = READ_BUF_SIZE / DEV_BSIZE;
 		/*
 		 * Ensure that the read size plus the leading offset does not
 		 * exceed the size of the read buffer.
 		 */
-		if (nb * DEV_BSIZE + diff > READ_BUF_SIZE)
-		    nb -= diff / DEV_BSIZE;
+		if (nb > (READ_BUF_SIZE - diff) / DEV_BSIZE)
+			nb = (READ_BUF_SIZE - diff) / DEV_BSIZE;
 		/*
 		 * Round the number of blocks to read up to the nearest multiple
 		 * of DEV_GELIBOOT_BSIZE.
 		 */
-		alignnb = nb + (diff / DEV_BSIZE) +
-		    (DEV_GELIBOOT_BSIZE / DEV_BSIZE - 1) & ~
-		    (unsigned int)(DEV_GELIBOOT_BSIZE / DEV_BSIZE - 1);
+		alignnb = roundup2(nb * DEV_BSIZE + diff, DEV_GELIBOOT_BSIZE)
+		    / DEV_BSIZE;
 
 		if (drvread(dsk, dmadat->rdbuf, alignlba, alignnb))
 			return -1;