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block: add -drive copy-on-read=on|off

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This patch adds the -drive copy-on-read=on|off command-line option:

  copy-on-read=on|off
  copy-on-read is "on" or "off" and enables whether to copy read backing
  file sectors into the image file.  Copy-on-read avoids accessing the
  same backing file sectors repeatedly and is useful when the backing
  file is over a slow network.  By default copy-on-read is off.

Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Stefan Hajnoczi 2011-11-17 13:40:32 +00:00 committed by Kevin Wolf
parent ab1859218a
commit fb0490f69f
4 changed files with 21 additions and 3 deletions
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6
blockdev.c
View File

@ -257,6 +257,7 @@ DriveInfo *drive_init(QemuOpts *opts, int default_to_scsi)
DriveInfo *dinfo;
BlockIOLimit io_limits;
int snapshot = 0;
bool copy_on_read;
int ret;
translation = BIOS_ATA_TRANSLATION_AUTO;
@ -273,6 +274,7 @@ DriveInfo *drive_init(QemuOpts *opts, int default_to_scsi)
snapshot = qemu_opt_get_bool(opts, "snapshot", 0);
ro = qemu_opt_get_bool(opts, "readonly", 0);
copy_on_read = qemu_opt_get_bool(opts, "copy-on-read", false);
file = qemu_opt_get(opts, "file");
serial = qemu_opt_get(opts, "serial");
@ -546,6 +548,10 @@ DriveInfo *drive_init(QemuOpts *opts, int default_to_scsi)
bdrv_flags |= (BDRV_O_SNAPSHOT|BDRV_O_CACHE_WB|BDRV_O_NO_FLUSH);
}
if (copy_on_read) {
bdrv_flags |= BDRV_O_COPY_ON_READ;
}
if (media == MEDIA_CDROM) {
/* CDROM is fine for any interface, don't check. */
ro = 1;

5
hmp-commands.hx
View File

@ -860,9 +860,10 @@ ETEXI
.args_type = "pci_addr:s,opts:s",
.params = "[[<domain>:]<bus>:]<slot>\n"
"[file=file][,if=type][,bus=n]\n"
"[,unit=m][,media=d][index=i]\n"
"[,unit=m][,media=d][,index=i]\n"
"[,cyls=c,heads=h,secs=s[,trans=t]]\n"
"[snapshot=on|off][,cache=on|off]",
"[,snapshot=on|off][,cache=on|off]\n"
"[,readonly=on|off][,copy-on-read=on|off]",
.help = "add drive to PCI storage controller",
.mhandler.cmd = drive_hot_add,
},

4
qemu-config.c
View File

@ -109,6 +109,10 @@ static QemuOptsList qemu_drive_opts = {
.name = "bps_wr",
.type = QEMU_OPT_NUMBER,
.help = "limit write bytes per second",
},{
.name = "copy-on-read",
.type = QEMU_OPT_BOOL,
.help = "copy read data from backing file into image file",
},
{ /* end of list */ }
},

9
qemu-options.hx
View File

@ -135,7 +135,7 @@ DEF("drive", HAS_ARG, QEMU_OPTION_drive,
" [,cyls=c,heads=h,secs=s[,trans=t]][,snapshot=on|off]\n"
" [,cache=writethrough|writeback|none|directsync|unsafe][,format=f]\n"
" [,serial=s][,addr=A][,id=name][,aio=threads|native]\n"
" [,readonly=on|off]\n"
" [,readonly=on|off][,copy-on-read=on|off]\n"
" [[,bps=b]|[[,bps_rd=r][,bps_wr=w]]][[,iops=i]|[[,iops_rd=r][,iops_wr=w]]\n"
" use 'file' as a drive image\n", QEMU_ARCH_ALL)
STEXI
@ -187,6 +187,9 @@ host disk is full; report the error to the guest otherwise).
The default setting is @option{werror=enospc} and @option{rerror=report}.
@item readonly
Open drive @option{file} as read-only. Guest write attempts will fail.
@item copy-on-read=@var{copy-on-read}
@var{copy-on-read} is "on" or "off" and enables whether to copy read backing
file sectors into the image file.
@end table
By default, writethrough caching is used for all block device. This means that
@ -218,6 +221,10 @@ like your host losing power, the disk storage getting disconnected accidently,
etc. you're image will most probably be rendered unusable. When using
the @option{-snapshot} option, unsafe caching is always used.
Copy-on-read avoids accessing the same backing file sectors repeatedly and is
useful when the backing file is over a slow network. By default copy-on-read
is off.
Instead of @option{-cdrom} you can use:
@example
qemu -drive file=file,index=2,media=cdrom