From: Linus Torvalds <torvalds@linux-foundation.org>
Date: Mon, 18 Jan 2010 23:09:21 +0000 (+0100)
Subject: libblkid: disable read-ahead when probing device files
X-Git-Url: https://err.no/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=07684fc3b1802e092ea60786418c9b75d99cb435;p=util-linux

libblkid: disable read-ahead when probing device files

Read-ahead doesn't work very well on device probing, and can hurt a lot
when we do essentially random accesses on very slow devices. So disable it
if possible.

[kzak@redhat.com: - add posix_fadvise() configure test]

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Karel Zak <kzak@redhat.com>
---

diff --git a/configure.ac b/configure.ac
index 5ddeaa5d..1fef9444 100644
--- a/configure.ac
+++ b/configure.ac
@@ -163,6 +163,7 @@ AC_CHECK_FUNCS(
 	setresuid \
 	inotify_init \
 	prctl \
+	posix_fadvise \
 	getmntinfo \
 	__secure_getenv \
 	rpmatch])
diff --git a/shlibs/blkid/src/probe.c b/shlibs/blkid/src/probe.c
index 2d3cafec..b2c96a6b 100644
--- a/shlibs/blkid/src/probe.c
+++ b/shlibs/blkid/src/probe.c
@@ -640,6 +640,10 @@ int blkid_probe_set_device(blkid_probe pr, int fd,
 	pr->mode = 0;
 	pr->blkssz = 0;
 
+#if defined(POSIX_FADV_RANDOM) && defined(HAVE_POSIX_FADVISE)
+	/* Disable read-ahead */
+	posix_fadvise(fd, 0, 0, POSIX_FADV_RANDOM);
+#endif
 	if (size)
 		pr->size = size;
 	else {