[Libguestfs] [PATCH] Revert "add_drive_ro adds readonly=on option if available." (RHBZ#617200).
Richard W.M. Jones
rjones at redhat.com
Thu Jul 22 13:46:05 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 004c0345d6fd9f141978f5163e053a67dba31cd0 Mon Sep 17 00:00:00 2001
From: Richard Jones <rjones at redhat.com>
Date: Thu, 22 Jul 2010 14:39:36 +0100
Subject: [PATCH] Revert "add_drive_ro adds readonly=on option if available." (RHBZ#617200).
Adding the readonly=on option is not so clever. This causes
qemu to present the disk as read-only to the guest. (The
expected behaviour of snapshots=on,readonly=on was that it
would open the disk O_RDONLY but present a writable disk to
the guest).
Since the guest sees a read-only disk, we are unable to do any
recovery if a filesystem on the disk is inconsistent. This basically
prevents most accesses to live disk images.
What we really want is a qemu option which presents a writable
disk to the guest, but only opens the disk on the host side with
O_RDONLY, to alleviate the udev bug RHBZ#571714.
This reverts commit 676462684e05dd8341dd695762dd99a87d8ec022.
---
src/generator.ml | 4 +---
src/guestfs.c | 22 ++++------------------
2 files changed, 5 insertions(+), 21 deletions(-)
diff --git a/src/generator.ml b/src/generator.ml
index 3af673d..ccbc13d 100755
--- a/src/generator.ml
+++ b/src/generator.ml
@@ -559,15 +559,13 @@ 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,readonly=on,if=...>.
+C<-drive file=filename,snapshot=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 85a042a..d6c8d60 100644
--- a/src/guestfs.c
+++ b/src/guestfs.c
@@ -836,6 +836,9 @@ 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;
@@ -846,24 +849,7 @@ guestfs__add_drive_ro_with_if (guestfs_h *g, const char *filename,
return -1;
}
- 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);
+ snprintf (buf, len, "file=%s,snapshot=on,if=%s", filename, drive_if);
return guestfs__config (g, "-drive", buf);
}
--
1.7.1
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