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qemu-img create: add 'nocow' option 

Add 'nocow' option so that users could have a chance to set NOCOW flag to
newly created files. It's useful on btrfs file system to enhance performance.

Btrfs has low performance when hosting VM images, even more when the guest
in those VM are also using btrfs as file system. One way to mitigate this bad
performance is to turn off COW attributes on VM files. Generally, there are
two ways to turn off NOCOW on btrfs: a) by mounting fs with nodatacow, then
all newly created files will be NOCOW. b) per file. Add the NOCOW file
attribute. It could only be done to empty or new files.

This patch tries the second way, according to the option, it could add NOCOW
per file.

For most block drivers, since the create file step is in raw-posix.c, so we
can do setting NOCOW flag ioctl in raw-posix.c only.

But there are some exceptions, like block/vpc.c and block/vdi.c, they are
creating file by calling qemu_open directly. For them, do the same setting
NOCOW flag ioctl work in them separately.

[Fixed up 082.out due to the new 'nocow' creation option
--Stefan]

Signed-off-by: Chunyan Liu <cyliu@suse.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
This commit is contained in:
Chunyan Liu 2014-06-30 14:29:58 +08:00 committed by Stefan Hajnoczi
parent 8698e110f8
commit 4ab1559085
9 changed files with 146 additions and 6 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

6
block/qed.c
View File

@ -567,7 +567,7 @@ static void bdrv_qed_close(BlockDriverState *bs)
static int qed_create(const char *filename, uint32_t cluster_size,
uint64_t image_size, uint32_t table_size,
const char *backing_file, const char *backing_fmt,
Error **errp)
QemuOpts *opts, Error **errp)
{
QEDHeader header = {
.magic = QED_MAGIC,
@ -586,7 +586,7 @@ static int qed_create(const char *filename, uint32_t cluster_size,
int ret = 0;
BlockDriverState *bs;
ret = bdrv_create_file(filename, NULL, &local_err);
ret = bdrv_create_file(filename, opts, &local_err);
if (ret < 0) {
error_propagate(errp, local_err);
return ret;
@ -682,7 +682,7 @@ static int bdrv_qed_create(const char *filename, QemuOpts *opts, Error **errp)
}
ret = qed_create(filename, cluster_size, image_size, table_size,
backing_file, backing_fmt, errp);
backing_file, backing_fmt, opts, errp);
finish:
g_free(backing_file);

25
block/raw-posix.c
View File

@ -55,6 +55,9 @@
#include <linux/cdrom.h>
#include <linux/fd.h>
#include <linux/fs.h>
#ifndef FS_NOCOW_FL
#define FS_NOCOW_FL 0x00800000 /* Do not cow file */
#endif
#endif
#ifdef CONFIG_FIEMAP
#include <linux/fiemap.h>
@ -1278,12 +1281,14 @@ static int raw_create(const char *filename, QemuOpts *opts, Error **errp)
int fd;
int result = 0;
int64_t total_size = 0;
bool nocow = false;
strstart(filename, "file:", &filename);
/* Read out options */
total_size =
qemu_opt_get_size_del(opts, BLOCK_OPT_SIZE, 0) / BDRV_SECTOR_SIZE;
nocow = qemu_opt_get_bool(opts, BLOCK_OPT_NOCOW, false);
fd = qemu_open(filename, O_WRONLY | O_CREAT | O_TRUNC | O_BINARY,
0644);
@ -1291,6 +1296,21 @@ static int raw_create(const char *filename, QemuOpts *opts, Error **errp)
result = -errno;
error_setg_errno(errp, -result, "Could not create file");
} else {
if (nocow) {
#ifdef __linux__
/* Set NOCOW flag to solve performance issue on fs like btrfs.
* This is an optimisation. The FS_IOC_SETFLAGS ioctl return value
* will be ignored since any failure of this operation should not
* block the left work.
*/
int attr;
if (ioctl(fd, FS_IOC_GETFLAGS, &attr) == 0) {
attr |= FS_NOCOW_FL;
ioctl(fd, FS_IOC_SETFLAGS, &attr);
}
#endif
}
if (ftruncate(fd, total_size * BDRV_SECTOR_SIZE) != 0) {
result = -errno;
error_setg_errno(errp, -result, "Could not resize file");
@ -1477,6 +1497,11 @@ static QemuOptsList raw_create_opts = {
.type = QEMU_OPT_SIZE,
.help = "Virtual disk size"
},
{
.name = BLOCK_OPT_NOCOW,
.type = QEMU_OPT_BOOL,
.help = "Turn off copy-on-write (valid only on btrfs)"
},
{ /* end of list */ }
}
};

29
block/vdi.c
View File

@ -53,6 +53,13 @@
#include "block/block_int.h"
#include "qemu/module.h"
#include "migration/migration.h"
#ifdef __linux__
#include <linux/fs.h>
#include <sys/ioctl.h>
#ifndef FS_NOCOW_FL
#define FS_NOCOW_FL 0x00800000 /* Do not cow file */
#endif
#endif
#if defined(CONFIG_UUID)
#include <uuid/uuid.h>
@ -683,6 +690,7 @@ static int vdi_create(const char *filename, QemuOpts *opts, Error **errp)
VdiHeader header;
size_t i;
size_t bmap_size;
bool nocow = false;
logout("\n");
@ -699,6 +707,7 @@ static int vdi_create(const char *filename, QemuOpts *opts, Error **errp)
image_type = VDI_TYPE_STATIC;
}
#endif
nocow = qemu_opt_get_bool_del(opts, BLOCK_OPT_NOCOW, false);
if (bytes > VDI_DISK_SIZE_MAX) {
result = -ENOTSUP;
@ -716,6 +725,21 @@ static int vdi_create(const char *filename, QemuOpts *opts, Error **errp)
goto exit;
}
if (nocow) {
#ifdef __linux__
/* Set NOCOW flag to solve performance issue on fs like btrfs.
* This is an optimisation. The FS_IOC_SETFLAGS ioctl return value will
* be ignored since any failure of this operation should not block the
* left work.
*/
int attr;
if (ioctl(fd, FS_IOC_GETFLAGS, &attr) == 0) {
attr |= FS_NOCOW_FL;
ioctl(fd, FS_IOC_SETFLAGS, &attr);
}
#endif
}
/* We need enough blocks to store the given disk size,
so always round up. */
blocks = (bytes + block_size - 1) / block_size;
@ -818,6 +842,11 @@ static QemuOptsList vdi_create_opts = {
.def_value_str = "off"
},
#endif
{
.name = BLOCK_OPT_NOCOW,
.type = QEMU_OPT_BOOL,
.help = "Turn off copy-on-write (valid only on btrfs)"
},
/* TODO: An additional option to set UUID values might be useful. */
{ /* end of list */ }
}

6
block/vmdk.c
View File

@ -1529,7 +1529,7 @@ static int coroutine_fn vmdk_co_write_zeroes(BlockDriverState *bs,
static int vmdk_create_extent(const char *filename, int64_t filesize,
bool flat, bool compress, bool zeroed_grain,
Error **errp)
QemuOpts *opts, Error **errp)
{
int ret, i;
BlockDriverState *bs = NULL;
@ -1539,7 +1539,7 @@ static int vmdk_create_extent(const char *filename, int64_t filesize,
uint32_t *gd_buf = NULL;
int gd_buf_size;
ret = bdrv_create_file(filename, NULL, &local_err);
ret = bdrv_create_file(filename, opts, &local_err);
if (ret < 0) {
error_propagate(errp, local_err);
goto exit;
@ -1845,7 +1845,7 @@ static int vmdk_create(const char *filename, QemuOpts *opts, Error **errp)
path, desc_filename);
if (vmdk_create_extent(ext_filename, size,
flat, compress, zeroed_grain, errp)) {
flat, compress, zeroed_grain, opts, errp)) {
ret = -EINVAL;
goto exit;
}

29
block/vpc.c
View File

@ -29,6 +29,13 @@
#if defined(CONFIG_UUID)
#include <uuid/uuid.h>
#endif
#ifdef __linux__
#include <linux/fs.h>
#include <sys/ioctl.h>
#ifndef FS_NOCOW_FL
#define FS_NOCOW_FL 0x00800000 /* Do not cow file */
#endif
#endif
/**************************************************************/
@ -751,6 +758,7 @@ static int vpc_create(const char *filename, QemuOpts *opts, Error **errp)
int64_t total_size;
int disk_type;
int ret = -EIO;
bool nocow = false;
/* Read out options */
total_size = qemu_opt_get_size_del(opts, BLOCK_OPT_SIZE, 0);
@ -767,6 +775,7 @@ static int vpc_create(const char *filename, QemuOpts *opts, Error **errp)
} else {
disk_type = VHD_DYNAMIC;
}
nocow = qemu_opt_get_bool_del(opts, BLOCK_OPT_NOCOW, false);
/* Create the file */
fd = qemu_open(filename, O_WRONLY | O_CREAT | O_TRUNC | O_BINARY, 0644);
@ -775,6 +784,21 @@ static int vpc_create(const char *filename, QemuOpts *opts, Error **errp)
goto out;
}
if (nocow) {
#ifdef __linux__
/* Set NOCOW flag to solve performance issue on fs like btrfs.
* This is an optimisation. The FS_IOC_SETFLAGS ioctl return value will
* be ignored since any failure of this operation should not block the
* left work.
*/
int attr;
if (ioctl(fd, FS_IOC_GETFLAGS, &attr) == 0) {
attr |= FS_NOCOW_FL;
ioctl(fd, FS_IOC_SETFLAGS, &attr);
}
#endif
}
/*
* Calculate matching total_size and geometry. Increase the number of
* sectors requested until we get enough (or fail). This ensures that
@ -884,6 +908,11 @@ static QemuOptsList vpc_create_opts = {
"Type of virtual hard disk format. Supported formats are "
"{dynamic (default) | fixed} "
},
{
.name = BLOCK_OPT_NOCOW,
.type = QEMU_OPT_BOOL,
.help = "Turn off copy-on-write (valid only on btrfs)"
},
{ /* end of list */ }
}
};

1
include/block/block_int.h
View File

@ -54,6 +54,7 @@
#define BLOCK_OPT_LAZY_REFCOUNTS "lazy_refcounts"
#define BLOCK_OPT_ADAPTER_TYPE "adapter_type"
#define BLOCK_OPT_REDUNDANCY "redundancy"
#define BLOCK_OPT_NOCOW "nocow"
typedef struct BdrvTrackedRequest {
BlockDriverState *bs;

16
qemu-doc.texi
View File

@ -589,6 +589,22 @@ check -r all} is required, which may take some time.
This option can only be enabled if @code{compat=1.1} is specified.
@item nocow
If this option is set to @code{on}, it will trun off COW of the file. It's only
valid on btrfs, no effect on other file systems.
Btrfs has low performance when hosting a VM image file, even more when the guest
on the VM also using btrfs as file system. Turning off COW is a way to mitigate
this bad performance. Generally there are two ways to turn off COW on btrfs:
a) Disable it by mounting with nodatacow, then all newly created files will be
NOCOW. b) For an empty file, add the NOCOW file attribute. That's what this option
does.
Note: this option is only valid to new or empty files. If there is an existing
file which is COW and has data blocks already, it couldn't be changed to NOCOW
by setting @code{nocow=on}. One can issue @code{lsattr filename} to check if
the NOCOW flag is set or not (Capitabl 'C' is NOCOW flag).
@end table
@item qed

16
qemu-img.texi
View File

@ -474,6 +474,22 @@ check -r all} is required, which may take some time.
This option can only be enabled if @code{compat=1.1} is specified.
@item nocow
If this option is set to @code{on}, it will trun off COW of the file. It's only
valid on btrfs, no effect on other file systems.
Btrfs has low performance when hosting a VM image file, even more when the guest
on the VM also using btrfs as file system. Turning off COW is a way to mitigate
this bad performance. Generally there are two ways to turn off COW on btrfs:
a) Disable it by mounting with nodatacow, then all newly created files will be
NOCOW. b) For an empty file, add the NOCOW file attribute. That's what this option
does.
Note: this option is only valid to new or empty files. If there is an existing
file which is COW and has data blocks already, it couldn't be changed to NOCOW
by setting @code{nocow=on}. One can issue @code{lsattr filename} to check if
the NOCOW flag is set or not (Capitabl 'C' is NOCOW flag).
@end table
@item Other

24
tests/qemu-iotests/082.out
View File

@ -66,6 +66,7 @@ encryption Encrypt the image
cluster_size qcow2 cluster size
preallocation Preallocation mode (allowed values: off, metadata)
lazy_refcounts Postpone refcount updates
nocow Turn off copy-on-write (valid only on btrfs)
Testing: create -f qcow2 -o ? TEST_DIR/t.qcow2 128M
Supported options:
@ -77,6 +78,7 @@ encryption Encrypt the image
cluster_size qcow2 cluster size
preallocation Preallocation mode (allowed values: off, metadata)
lazy_refcounts Postpone refcount updates
nocow Turn off copy-on-write (valid only on btrfs)
Testing: create -f qcow2 -o cluster_size=4k,help TEST_DIR/t.qcow2 128M
Supported options:
@ -88,6 +90,7 @@ encryption Encrypt the image
cluster_size qcow2 cluster size
preallocation Preallocation mode (allowed values: off, metadata)
lazy_refcounts Postpone refcount updates
nocow Turn off copy-on-write (valid only on btrfs)
Testing: create -f qcow2 -o cluster_size=4k,? TEST_DIR/t.qcow2 128M
Supported options:
@ -99,6 +102,7 @@ encryption Encrypt the image
cluster_size qcow2 cluster size
preallocation Preallocation mode (allowed values: off, metadata)
lazy_refcounts Postpone refcount updates
nocow Turn off copy-on-write (valid only on btrfs)
Testing: create -f qcow2 -o help,cluster_size=4k TEST_DIR/t.qcow2 128M
Supported options:
@ -110,6 +114,7 @@ encryption Encrypt the image
cluster_size qcow2 cluster size
preallocation Preallocation mode (allowed values: off, metadata)
lazy_refcounts Postpone refcount updates
nocow Turn off copy-on-write (valid only on btrfs)
Testing: create -f qcow2 -o ?,cluster_size=4k TEST_DIR/t.qcow2 128M
Supported options:
@ -121,6 +126,7 @@ encryption Encrypt the image
cluster_size qcow2 cluster size
preallocation Preallocation mode (allowed values: off, metadata)
lazy_refcounts Postpone refcount updates
nocow Turn off copy-on-write (valid only on btrfs)
Testing: create -f qcow2 -o cluster_size=4k -o help TEST_DIR/t.qcow2 128M
Supported options:
@ -132,6 +138,7 @@ encryption Encrypt the image
cluster_size qcow2 cluster size
preallocation Preallocation mode (allowed values: off, metadata)
lazy_refcounts Postpone refcount updates
nocow Turn off copy-on-write (valid only on btrfs)
Testing: create -f qcow2 -o cluster_size=4k -o ? TEST_DIR/t.qcow2 128M
Supported options:
@ -143,6 +150,7 @@ encryption Encrypt the image
cluster_size qcow2 cluster size
preallocation Preallocation mode (allowed values: off, metadata)
lazy_refcounts Postpone refcount updates
nocow Turn off copy-on-write (valid only on btrfs)
Testing: create -f qcow2 -o backing_file=TEST_DIR/t.qcow2,,help TEST_DIR/t.qcow2 128M
Formatting 'TEST_DIR/t.qcow2', fmt=qcow2 size=134217728 backing_file='TEST_DIR/t.qcow2,help' encryption=off cluster_size=65536 lazy_refcounts=off
@ -247,6 +255,7 @@ encryption Encrypt the image
cluster_size qcow2 cluster size
preallocation Preallocation mode (allowed values: off, metadata)
lazy_refcounts Postpone refcount updates
nocow Turn off copy-on-write (valid only on btrfs)
Testing: convert -O qcow2 -o ? TEST_DIR/t.qcow2 TEST_DIR/t.qcow2.base
Supported options:
@ -258,6 +267,7 @@ encryption Encrypt the image
cluster_size qcow2 cluster size
preallocation Preallocation mode (allowed values: off, metadata)
lazy_refcounts Postpone refcount updates
nocow Turn off copy-on-write (valid only on btrfs)
Testing: convert -O qcow2 -o cluster_size=4k,help TEST_DIR/t.qcow2 TEST_DIR/t.qcow2.base
Supported options:
@ -269,6 +279,7 @@ encryption Encrypt the image
cluster_size qcow2 cluster size
preallocation Preallocation mode (allowed values: off, metadata)
lazy_refcounts Postpone refcount updates
nocow Turn off copy-on-write (valid only on btrfs)
Testing: convert -O qcow2 -o cluster_size=4k,? TEST_DIR/t.qcow2 TEST_DIR/t.qcow2.base
Supported options:
@ -280,6 +291,7 @@ encryption Encrypt the image
cluster_size qcow2 cluster size
preallocation Preallocation mode (allowed values: off, metadata)
lazy_refcounts Postpone refcount updates
nocow Turn off copy-on-write (valid only on btrfs)
Testing: convert -O qcow2 -o help,cluster_size=4k TEST_DIR/t.qcow2 TEST_DIR/t.qcow2.base
Supported options:
@ -291,6 +303,7 @@ encryption Encrypt the image
cluster_size qcow2 cluster size
preallocation Preallocation mode (allowed values: off, metadata)
lazy_refcounts Postpone refcount updates
nocow Turn off copy-on-write (valid only on btrfs)
Testing: convert -O qcow2 -o ?,cluster_size=4k TEST_DIR/t.qcow2 TEST_DIR/t.qcow2.base
Supported options:
@ -302,6 +315,7 @@ encryption Encrypt the image
cluster_size qcow2 cluster size
preallocation Preallocation mode (allowed values: off, metadata)
lazy_refcounts Postpone refcount updates
nocow Turn off copy-on-write (valid only on btrfs)
Testing: convert -O qcow2 -o cluster_size=4k -o help TEST_DIR/t.qcow2 TEST_DIR/t.qcow2.base
Supported options:
@ -313,6 +327,7 @@ encryption Encrypt the image
cluster_size qcow2 cluster size
preallocation Preallocation mode (allowed values: off, metadata)
lazy_refcounts Postpone refcount updates
nocow Turn off copy-on-write (valid only on btrfs)
Testing: convert -O qcow2 -o cluster_size=4k -o ? TEST_DIR/t.qcow2 TEST_DIR/t.qcow2.base
Supported options:
@ -324,6 +339,7 @@ encryption Encrypt the image
cluster_size qcow2 cluster size
preallocation Preallocation mode (allowed values: off, metadata)
lazy_refcounts Postpone refcount updates
nocow Turn off copy-on-write (valid only on btrfs)
Testing: convert -O qcow2 -o backing_file=TEST_DIR/t.qcow2,,help TEST_DIR/t.qcow2 TEST_DIR/t.qcow2.base
qemu-img: Could not open 'TEST_DIR/t.qcow2.base': Could not open backing file: Could not open 'TEST_DIR/t.qcow2,help': No such file or directory
@ -417,6 +433,7 @@ encryption Encrypt the image
cluster_size qcow2 cluster size
preallocation Preallocation mode (allowed values: off, metadata)
lazy_refcounts Postpone refcount updates
nocow Turn off copy-on-write (valid only on btrfs)
Testing: amend -f qcow2 -o ? TEST_DIR/t.qcow2
Supported options:
@ -428,6 +445,7 @@ encryption Encrypt the image
cluster_size qcow2 cluster size
preallocation Preallocation mode (allowed values: off, metadata)
lazy_refcounts Postpone refcount updates
nocow Turn off copy-on-write (valid only on btrfs)
Testing: amend -f qcow2 -o cluster_size=4k,help TEST_DIR/t.qcow2
Supported options:
@ -439,6 +457,7 @@ encryption Encrypt the image
cluster_size qcow2 cluster size
preallocation Preallocation mode (allowed values: off, metadata)
lazy_refcounts Postpone refcount updates
nocow Turn off copy-on-write (valid only on btrfs)
Testing: amend -f qcow2 -o cluster_size=4k,? TEST_DIR/t.qcow2
Supported options:
@ -450,6 +469,7 @@ encryption Encrypt the image
cluster_size qcow2 cluster size
preallocation Preallocation mode (allowed values: off, metadata)
lazy_refcounts Postpone refcount updates
nocow Turn off copy-on-write (valid only on btrfs)
Testing: amend -f qcow2 -o help,cluster_size=4k TEST_DIR/t.qcow2
Supported options:
@ -461,6 +481,7 @@ encryption Encrypt the image
cluster_size qcow2 cluster size
preallocation Preallocation mode (allowed values: off, metadata)
lazy_refcounts Postpone refcount updates
nocow Turn off copy-on-write (valid only on btrfs)
Testing: amend -f qcow2 -o ?,cluster_size=4k TEST_DIR/t.qcow2
Supported options:
@ -472,6 +493,7 @@ encryption Encrypt the image
cluster_size qcow2 cluster size
preallocation Preallocation mode (allowed values: off, metadata)
lazy_refcounts Postpone refcount updates
nocow Turn off copy-on-write (valid only on btrfs)
Testing: amend -f qcow2 -o cluster_size=4k -o help TEST_DIR/t.qcow2
Supported options:
@ -483,6 +505,7 @@ encryption Encrypt the image
cluster_size qcow2 cluster size
preallocation Preallocation mode (allowed values: off, metadata)
lazy_refcounts Postpone refcount updates
nocow Turn off copy-on-write (valid only on btrfs)
Testing: amend -f qcow2 -o cluster_size=4k -o ? TEST_DIR/t.qcow2
Supported options:
@ -494,6 +517,7 @@ encryption Encrypt the image
cluster_size qcow2 cluster size
preallocation Preallocation mode (allowed values: off, metadata)
lazy_refcounts Postpone refcount updates
nocow Turn off copy-on-write (valid only on btrfs)
Testing: amend -f qcow2 -o backing_file=TEST_DIR/t.qcow2,,help TEST_DIR/t.qcow2