On (Thu) Mar 19 2009 [20:17:52], Amit Shah wrote:
> This patchset makes use of the posix_fallocate() call to allocate
> chunks of files whenever needed if it's available.
>
> We fallback to using safewrite() if it's not available.
>
> mmap() could be used instead of safewrite too; I have a patch in case
> someone is interested in seeing it.
Something like this:
>From d33b843b381ea6a25c6e8efb6b248965a40e5f84 Mon Sep 17 00:00:00 2001
From: Amit Shah <amit.shah@xxxxxxxxxx>
Date: Thu, 19 Mar 2009 21:43:50 +0530
Subject: [PATCH] Use mmap() and memset() for safezero
If available, use mmap to allocate zeroed chunks for files. This
should be faster than allocating small chunks using safewrite.
Signed-off-by: Amit Shah <amit.shah@xxxxxxxxxx>
---
configure.in | 2 +-
src/util.c | 32 +++++++++++++++++++++++++++++++-
2 files changed, 32 insertions(+), 2 deletions(-)
diff --git a/configure.in b/configure.in
index edce040..6b2bb5e 100644
--- a/configure.in
+++ b/configure.in
@@ -72,7 +72,7 @@ dnl Use --disable-largefile if you don't want this.
AC_SYS_LARGEFILE
dnl Availability of various common functions (non-fatal if missing).
-AC_CHECK_FUNCS([cfmakeraw regexec uname sched_getaffinity getuid getgid posix_fallocate])
+AC_CHECK_FUNCS([cfmakeraw regexec uname sched_getaffinity getuid getgid posix_fallocate mmap])
dnl Availability of various not common threadsafe functions
AC_CHECK_FUNCS([strerror_r strtok_r getmntent_r getgrnam_r getpwuid_r])
diff --git a/src/util.c b/src/util.c
index 955c4e5..93d2937 100644
--- a/src/util.c
+++ b/src/util.c
@@ -39,6 +39,9 @@
#if HAVE_SYS_WAIT_H
#include <sys/wait.h>
#endif
+#if HAVE_MMAP
+#include <sys/mman.h>
+#endif
#include <string.h>
#include <signal.h>
#if HAVE_TERMIOS_H
@@ -123,6 +126,32 @@ int safezero(int fd, int flags, off_t offset, off_t len)
return posix_fallocate(fd, offset, len);
}
#else
+
+#ifdef HAVE_MMAP
+int safezero(int fd, int flags, off_t offset, off_t len)
+{
+ int r;
+ char *buf;
+
+ /* memset wants the mmap'ed file to be present on disk so create a
+ * sparse file
+ */
+ r = ftruncate(fd, len);
+ if (r < 0)
+ return -errno;
+
+ buf = mmap(NULL, len, PROT_READ | PROT_WRITE, MAP_SHARED, fd, offset);
+ if (buf == MAP_FAILED)
+ return -errno;
+
+ memset(buf, 0, len);
+ munmap(buf, len);
+
+ return 0;
+}
+
+#else /* HAVE_MMAP */
+
int safezero(int fd, int flags, off_t offset, off_t len)
{
int r;
@@ -153,7 +182,8 @@ int safezero(int fd, int flags, off_t offset, off_t len)
VIR_FREE(buf);
return 0;
}
-#endif
+#endif /* HAVE_MMAP */
+#endif /* HAVE_POSIX_FALLOCATE */
#ifndef PROXY
--
1.6.0.6
--
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