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authorStefan Hajnoczi <stefanha@linux.vnet.ibm.com>2011-11-17 13:40:32 +0000
committerKevin Wolf <kwolf@redhat.com>2011-12-05 14:51:38 +0100
commitfb0490f69feb96b7e92457f176dc834ff0b00b09 (patch)
tree78f832101d9988753dac64f1f47946f2fa306a97
parentab1859218a95977dc6881fcccce328d8146a6bdb (diff)
downloadqemu-arm-fb0490f69feb96b7e92457f176dc834ff0b00b09.tar.gz
block: add -drive copy-on-read=on|off
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>
-rw-r--r--blockdev.c6
-rw-r--r--hmp-commands.hx5
-rw-r--r--qemu-config.c4
-rw-r--r--qemu-options.hx9
4 files changed, 21 insertions, 3 deletions
diff --git a/blockdev.c b/blockdev.c
index 9068c5b1d0..af4e239b93 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -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;
diff --git a/hmp-commands.hx b/hmp-commands.hx
index f8d855e3be..79a919526d 100644
--- a/hmp-commands.hx
+++ b/hmp-commands.hx
@@ -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,
},
diff --git a/qemu-config.c b/qemu-config.c
index 1aa080fbcb..18f30204a1 100644
--- a/qemu-config.c
+++ b/qemu-config.c
@@ -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 */ }
},
diff --git a/qemu-options.hx b/qemu-options.hx
index 25a7be7948..b3db10c0ad 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -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