4:14 p.m.
[For a bug noted earlier by both Matt Booth and Jim Meyering]
If you use the guestfs_add_drive function, then currently it
generates a qemu command line element like:
-drive ...,cache=off,...
This causes qemu to try to open the device with O_DIRECT.
Unfortunately some filesystems don't support this flag, notably tmpfs,
which means you can't use libguestfs in conjunction with tmpfs. On
some systems /tmp is a tmpfs filesystem.
This patch fixes this so that if the filesystem doesn't support
O_DIRECT, then we omit the cache=off parameter. This seems reasonable
from a reliability point of view, because if you're using tmpfs then
you probably didn't expect reliability in the case where your system
suddenly powers off.
Tested using a tmpfs. Without:
$ guestfish alloc /mnt/tmp/test.img 10M : run
qemu: could not open disk image /mnt/tmp/test.img
libguestfs: error: connect: Connection refused
libguestfs: error: connect: Connection refused
libguestfs: error: connect: Connection refused
libguestfs: error: connect: Connection refused
With:
$ ./fish/guestfish
Welcome to guestfish, the libguestfs filesystem interactive shell for
editing virtual machine filesystems.
Type: 'help' for help with commands
'quit' to quit the shell
<fs> alloc /mnt/tmp/test.img 10M
<fs> run
<fs>
Rich.
--
Richard Jones, Emerging Technologies, Red Hat http://et.redhat.com/~rjones
libguestfs lets you edit virtual machines. Supports shell scripting,
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4:58 a.m.
On 12/08/09 22:14, Richard W.M. Jones wrote:
diff --git a/src/generator.ml b/src/generator.ml
index b9544ff..fa1f483 100755
--- a/src/generator.ml
+++ b/src/generator.ml
@@ -454,6 +454,8 @@ image).
This is equivalent to the qemu parameter
C<-drive file=filename,cache=off,if=...>.
+C<cache=off> is omitted in cases where it is not supported by
+the underlying filesystem.
Note that this call checks for the existence of C<filename>. This
stops you from specifying other types of drive which are supported
diff --git a/src/guestfs.c b/src/guestfs.c
index 37869e8..7f309c9 100644
--- a/src/guestfs.c
+++ b/src/guestfs.c
@@ -793,20 +793,38 @@ guestfs_add_drive (guestfs_h *g, const char *filename)
{
size_t len = strlen (filename) + 64;
char buf[len];
+ int fd;
I thought we'd decided to go with 'inline' declarations, whatever the
appropriate term for those is.
if (strchr (filename, ',') != NULL) {
error (g, _("filename cannot contain ',' (comma) character"));
return -1;
}
- if (access (filename, F_OK) == -1) {
- perrorf (g, "%s", filename);
- return -1;
+ /* cache=off improves reliability in the event of a host crash.
+ *
+ * However this option causes qemu to try to open the file with
+ * O_DIRECT. This fails on some filesystem types (notably tmpfs).
+ * So we check if we can open the file with or without O_DIRECT,
+ * and use cache=off (or not) accordingly.
+ *
+ * This test also checks for the presence of the file, which
+ * is a documented semantic of this interface.
+ */
+ fd = open (filename, O_RDONLY|O_DIRECT);
+ if (fd>= 0) {
+ close (fd);
+ snprintf (buf, len, "file=%s,cache=off,if=" DRIVE_IF, filename);
+ } else {
+ fd = open (filename, O_RDONLY);
+ if (fd>= 0) {
+ close (fd);
+ snprintf (buf, len, "file=%s,if=" DRIVE_IF, filename);
+ } else {
+ perrorf (g, "%s", filename);
+ return -1;
+ }
}
- /* cache=off improves reliability in the event of a host crash. */
- snprintf (buf, len, "file=%s,cache=off,if=%s", filename, DRIVE_IF);
-
return guestfs_config (g, "-drive", buf);
}
-- 1.6.2.5
ACK.
Matt
--
Matthew Booth, RHCA, RHCSS
Red Hat Engineering, Virtualisation Team
M: +44 (0)7977 267231
GPG ID: D33C3490
GPG FPR: 3733 612D 2D05 5458 8A8A 1600 3441 EA19 D33C 3490
5:11 a.m.
I pushed this one with the small change that Matt requested.
Rich.
--
Richard Jones, Emerging Technologies, Red Hat http://et.redhat.com/~rjones
New in Fedora 11: Fedora Windows cross-compiler. Compile Windows
programs, test, and build Windows installers. Over 70 libraries supprt'd
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