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From: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
To: qemu-devel@nongnu.org
Cc: Kevin Wolf <kwolf@redhat.com>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Marcelo Tosatti <mtosatti@redhat.com>,
	Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
Subject: [Qemu-devel] [RFC 6/6] block: add -drive copy-on-read=on|off
Date: Mon, 17 Oct 2011 16:47:32 +0100	[thread overview]
Message-ID: <1318866452-30026-7-git-send-email-stefanha@linux.vnet.ibm.com> (raw)
In-Reply-To: <1318866452-30026-1-git-send-email-stefanha@linux.vnet.ibm.com>

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>
---
 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

  parent reply	other threads:[~2011-10-17 15:47 UTC|newest]

Thread overview: 30+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-10-17 15:47 [Qemu-devel] [RFC 0/6] block: generic copy-on-read Stefan Hajnoczi
2011-10-17 15:47 ` [Qemu-devel] [RFC 1/6] block: add request tracking Stefan Hajnoczi
2011-11-02 16:30   ` Kevin Wolf
2011-11-03  7:57     ` Stefan Hajnoczi
2011-11-07 11:00   ` Zhi Yong Wu
2011-11-07 11:41     ` Stefan Hajnoczi
2011-11-08  6:13       ` Zhi Yong Wu
2011-10-17 15:47 ` [Qemu-devel] [RFC 2/6] block: add bdrv_set_copy_on_read() Stefan Hajnoczi
2011-11-02 16:36   ` Kevin Wolf
2011-11-03  8:01     ` Stefan Hajnoczi
2011-10-17 15:47 ` [Qemu-devel] [RFC 3/6] block: wait for overlapping requests Stefan Hajnoczi
2011-10-18 13:48   ` Marcelo Tosatti
2011-10-20 17:34     ` Stefan Hajnoczi
2011-11-03 14:17   ` Kevin Wolf
2011-10-17 15:47 ` [Qemu-devel] [RFC 4/6] block: request overlap detection Stefan Hajnoczi
2011-11-07 11:49   ` Zhi Yong Wu
2011-11-07 14:37     ` Stefan Hajnoczi
2011-11-08  6:34       ` Zhi Yong Wu
2011-11-08  8:16         ` Stefan Hajnoczi
2011-11-08  9:49           ` Zhi Yong Wu
2011-10-17 15:47 ` [Qemu-devel] [RFC 5/6] block: core copy-on-read logic Stefan Hajnoczi
2011-10-18 14:00   ` Marcelo Tosatti
2011-10-20 17:40     ` Stefan Hajnoczi
2011-10-18 14:03   ` Marcelo Tosatti
2011-11-03 14:30   ` Kevin Wolf
2011-10-17 15:47 ` Stefan Hajnoczi [this message]
2011-11-03 14:32   ` [Qemu-devel] [RFC 6/6] block: add -drive copy-on-read=on|off Kevin Wolf
2011-11-03 16:21     ` Stefan Hajnoczi
2011-11-01 14:28 ` [Qemu-devel] [RFC 0/6] block: generic copy-on-read Stefan Hajnoczi
2011-11-01 15:07   ` Marcelo Tosatti

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