From: Roman Mamedov <rm@romanrm.ru>
To: dima <dolenin@parallels.com>
Cc: <linux-btrfs@vger.kernel.org>
Subject: Re: Set nodatacow per file?
Date: Mon, 13 Feb 2012 14:09:21 +0600 [thread overview]
Message-ID: <20120213140921.5a009404@natsu> (raw)
In-Reply-To: <4F38BE53.4080204@parallels.com>
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On Mon, 13 Feb 2012 16:40:03 +0900
dima <dolenin@parallels.com> wrote:
> Hello Ralf-Peter,
>
> Actually it is possible. Check out David's response to my question from
> some time ago:
> http://permalink.gmane.org/gmane.comp.file-systems.btrfs/14227
>
> The nocow.c script he attached does just the thing you want. The script
> is really working. I needed nocow for different purpose but it did not
> occur to me to try it on VM image and see if the performance would
> improve. Sounds like a great idea. If you get around to try it, pls.
> post your impressions here.
Thanks for the link, this is indeed interesting.
I made a couple of small changes, i.e. I wanted a way to unset nocow and to
check that changing flags really worked.
gcc -o /usr/local/bin/nocow nocow.c
ln -sf /usr/local/bin/nocow /usr/local/bin/cow
Perhaps the support for setting this flag should be added to the 'btrfs'
utility.
--
With respect,
Roman
~~~~~~~~~~~~~~~~~~~~~~~~~~~
"Stallman had a printer,
with code he could not see.
So he began to tinker,
and set the software free."
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#include <fcntl.h>
#include <stdlib.h>
#include <sys/ioctl.h>
#include <string.h>
#include <linux/types.h>
#include <stdio.h>
#include <errno.h>
#ifndef FS_IOC_SETFLAGS
#define FS_IOC_SETFLAGS _IOW('f', 2, long)
#warning defining SETFLAGS locally
#endif
#ifndef FS_IOC_GETFLAGS
#define FS_IOC_GETFLAGS _IOR('f', 1, long)
#warning defining GETFLAGS locally
#endif
#ifndef FS_NOCOW_FL
#define FS_NOCOW_FL 0x00800000 /* Do not cow file */
#endif
int main(int argc, char **argv)
{
int fd;
int r;
long flags;
if (argc < 2) {
printf("usage: %s file\n", argv[0]);
exit(1);
}
fd = open(argv[1], O_RDONLY);
if (fd == -1) {
perror("open()");
return 1;
}
printf("GETFLAGS ioctl 0x%x\n", FS_IOC_GETFLAGS);
printf("SETFLAGS ioctl 0x%x\n", FS_IOC_SETFLAGS);
r = ioctl(fd, FS_IOC_GETFLAGS, &flags);
if (r == -1) {
perror("ioctl(GETFLAGS)");
return 1;
} else {
printf("file flags before: 0x%lx\n", flags);
}
if(strcmp(argv[0], "cow")==0) {
printf("Remove NOCOW flag for %s\n", argv[1]);
flags ^= FS_NOCOW_FL;
} else {
printf("Set NOCOW flag for %s\n", argv[1]);
flags |= FS_NOCOW_FL;
}
r = ioctl(fd, FS_IOC_SETFLAGS, &flags);
printf("ioctl returned: %d\n", r);
if (r == -1) {
perror("ioctl()");
return 1;
}
r = ioctl(fd, FS_IOC_GETFLAGS, &flags);
if (r == -1) {
perror("ioctl(GETFLAGS)");
return 1;
} else {
printf("file flags after: 0x%lx\n", flags);
}
return 0;
}
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next prev parent reply other threads:[~2012-02-13 8:09 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-02-13 7:17 Set nodatacow per file? Ralf-Peter Rohbeck
2012-02-13 7:34 ` Chester
2012-02-13 8:10 ` Liu Bo
2012-02-13 7:40 ` dima
2012-02-13 8:09 ` Roman Mamedov [this message]
2012-02-13 8:40 ` dima
2012-02-13 13:42 ` dima
2012-02-13 13:51 ` Roman Mamedov
2012-02-13 14:31 ` Dmitry Olenin
2012-02-13 14:10 ` David Sterba
2012-02-13 14:21 ` Timo Witte
2012-02-13 15:10 ` dima
2012-02-16 13:55 ` NOCOW + compress-force = bug Roman Mamedov
2012-02-16 14:30 ` David Sterba
2012-02-16 17:58 ` Chris Mason
2012-03-13 18:11 ` Jeff Mahoney
2012-03-13 18:36 ` Jeff Mahoney
2012-02-29 15:09 ` Set nodatacow per file? Kyle Gates
2012-02-29 15:34 ` cwillu
2012-02-24 5:22 ` dima
2012-02-27 13:54 ` dima
2012-02-27 22:10 ` Chester
2012-02-28 0:51 ` dima
2012-03-02 3:28 ` dima
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