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 <stefa...@linux.vnet.ibm.com> --- blockdev.c | 6 ++++++ hmp-commands.hx | 5 +++-- qemu-config.c | 4 ++++ qemu-options.hx | 9 ++++++++- 4 files changed, 21 insertions(+), 3 deletions(-) diff --git a/blockdev.c b/blockdev.c index 0827bf7..1dd0f23 100644 --- a/blockdev.c +++ b/blockdev.c @@ -236,6 +236,7 @@ DriveInfo *drive_init(QemuOpts *opts, int default_to_scsi) const char *devaddr; DriveInfo *dinfo; int snapshot = 0; + int copy_on_read; int ret; translation = BIOS_ATA_TRANSLATION_AUTO; @@ -252,6 +253,7 @@ 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", 0); file = qemu_opt_get(opts, "file"); serial = qemu_opt_get(opts, "serial"); @@ -502,6 +504,10 @@ 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 ab08d58..05a1498 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 7a7854f..fbe4f6a 100644 --- a/qemu-config.c +++ b/qemu-config.c @@ -85,6 +85,10 @@ static QemuOptsList qemu_drive_opts = { .name = "readonly", .type = QEMU_OPT_BOOL, .help = "open drive file as read-only", + },{ + .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 dfbabd0..c0bf856 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" " use 'file' as a drive image\n", QEMU_ARCH_ALL) STEXI @item -drive @var{option}[,@var{option}[,@var{option}[,...]]] @@ -183,6 +183,9 @@ 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 @@ -214,6 +217,10 @@ 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 -- 1.7.6.3