[Libguestfs] [PATCH 2/2] add_drive_ro adds readonly=on option if available.
Richard W.M. Jones
rjones at redhat.com
Tue Mar 16 21:53:10 UTC 2010
--
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
virt-p2v converts physical machines to virtual machines. Boot with a
live CD or over the network (PXE) and turn machines into Xen guests.
http://et.redhat.com/~rjones/virt-p2v
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>From 676462684e05dd8341dd695762dd99a87d8ec022 Mon Sep 17 00:00:00 2001
From: Richard Jones <rjones at redhat.com>
Date: Tue, 16 Mar 2010 21:50:13 +0000
Subject: [PATCH 2/2] add_drive_ro adds readonly=on option if available.
Change the add_drive_ro call so it adds the readonly=on option
if qemu supports that.
This just means that qemu will not try to open the drive with
O_RDWR, and should not otherwise change the behaviour of qemu or
libguestfs. (In particular, writes to the read-only drive are
still permitted, and are just discarded when the handle is closed).
However it should alleviate RHBZ#571714 where udev was deciding
to incorrectly relabel a device because we had opened the device
for writing (even though we didn't actually write to it).
---
src/generator.ml | 4 +++-
src/guestfs.c | 22 ++++++++++++++++++----
2 files changed, 21 insertions(+), 5 deletions(-)
diff --git a/src/generator.ml b/src/generator.ml
index 4f569ba..83f307b 100755
--- a/src/generator.ml
+++ b/src/generator.ml
@@ -544,13 +544,15 @@ handle is closed. We don't currently have any method to enable
changes to be committed, although qemu can support this.
This is equivalent to the qemu parameter
-C<-drive file=filename,snapshot=on,if=...>.
+C<-drive file=filename,snapshot=on,readonly=on,if=...>.
C<if=...> is set at compile time by the configuration option
C<./configure --with-drive-if=...>. In the rare case where you
might need to change this at run time, use C<guestfs_add_drive_with_if>
or C<guestfs_add_drive_ro_with_if>.
+C<readonly=on> is only added where qemu supports this option.
+
Note that this call checks for the existence of C<filename>. This
stops you from specifying other types of drive which are supported
by qemu such as C<nbd:> and C<http:> URLs. To specify those, use
diff --git a/src/guestfs.c b/src/guestfs.c
index af60699..02d5fdb 100644
--- a/src/guestfs.c
+++ b/src/guestfs.c
@@ -792,9 +792,6 @@ int
guestfs__add_drive_ro_with_if (guestfs_h *g, const char *filename,
const char *drive_if)
{
- size_t len = strlen (filename) + 64;
- char buf[len];
-
if (strchr (filename, ',') != NULL) {
error (g, _("filename cannot contain ',' (comma) character"));
return -1;
@@ -805,7 +802,24 @@ guestfs__add_drive_ro_with_if (guestfs_h *g, const char *filename,
return -1;
}
- snprintf (buf, len, "file=%s,snapshot=on,if=%s", filename, drive_if);
+ if (qemu_supports (g, NULL) == -1)
+ return -1;
+
+ /* Only SCSI and virtio drivers support readonly mode.
+ * This is only supported as a QEMU feature since 2010/01.
+ */
+ int supports_ro = 0;
+ if ((STREQ (drive_if, "scsi") || STREQ (drive_if, "virtio")) &&
+ qemu_supports (g, "readonly=on"))
+ supports_ro = 1;
+
+ size_t len = strlen (filename) + 100;
+ char buf[len];
+
+ snprintf (buf, len, "file=%s,snapshot=on,%sif=%s",
+ filename,
+ supports_ro ? "readonly=on," : "",
+ drive_if);
return guestfs__config (g, "-drive", buf);
}
--
1.7.0.1
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