Date: Tue, 28 Mar 2000 10:09:44 -0600 (CST) From: dnelson@emsphone.com To: FreeBSD-gnats-submit@freebsd.org Subject: bin/17640: lseek+read -> pread Message-ID: <200003281609.KAA93423@dan.emsphone.com>
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>Number: 17640
>Category: bin
>Synopsis: lseek+read -> pread
>Confidential: no
>Severity: non-critical
>Priority: low
>Responsible: freebsd-bugs
>State: open
>Quarter:
>Keywords:
>Date-Required:
>Class: change-request
>Submitter-Id: current-users
>Arrival-Date: Tue Mar 28 08:10:00 PST 2000
>Closed-Date:
>Last-Modified:
>Originator: Dan Nelson
>Release: FreeBSD 5.0-CURRENT i386
>Organization:
Executive Marketing Services, Inc.
>Environment:
FreeBSD dan.emsphone.com 5.0-CURRENT FreeBSD 5.0-CURRENT #52: Mon Mar 20 10:01:54 CST 2000 dan@dan.emsphone.com:/usr/src/sys/compile/DANSMP i386
, but applies to 4.0 and 3.* as well.
>Description:
Simple replacement of an lseek()/read() combo with a single pread().
Halves the number of syscalls.
>How-To-Repeat:
>Fix:
I've been running the following code for a couple months, and both dump
and fsck work fine.
Index: sbin/dump/traverse.c
===================================================================
RCS file: /home/ncvs/src/sbin/dump/traverse.c,v
retrieving revision 1.10
diff -b -u -r1.10 traverse.c
--- sbin/dump/traverse.c 1999/08/28 00:12:39 1.10
+++ sbin/dump/traverse.c 2000/03/24 05:33:51
@@ -556,10 +556,7 @@
extern int errno;
loop:
- if (lseek(diskfd, ((off_t)blkno << dev_bshift), 0) !=
- ((off_t)blkno << dev_bshift))
- msg("bread: lseek fails\n");
- if ((cnt = read(diskfd, buf, size)) == size)
+ if ((cnt = pread(diskfd, buf, size, (off_t)blkno << dev_bshift)) == size)
return;
if (blkno + (size / dev_bsize) > fsbtodb(sblock, sblock->fs_size)) {
/*
Index: sbin/fsck/utilities.c
===================================================================
RCS file: /home/ncvs/src/sbin/fsck/utilities.c,v
retrieving revision 1.11
diff -b -u -r1.11 utilities.c
--- sbin/fsck/utilities.c 1999/08/28 00:12:49 1.11
+++ sbin/fsck/utilities.c 1999/11/25 05:54:06
@@ -327,11 +327,9 @@
offset = blk;
offset *= dev_bsize;
- if (lseek(fd, offset, 0) < 0)
- rwerror("SEEK", blk);
- else if (read(fd, buf, (int)size) == size)
+ if (pread(fd, buf, (int)size, offset) == size)
return (0);
- rwerror("READ", blk);
+ rwerror("PREAD", blk);
if (lseek(fd, offset, 0) < 0)
rwerror("SEEK", blk);
errs = 0;
>Release-Note:
>Audit-Trail:
>Unformatted:
Dan Nelson
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