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launch: libvirt: Autodetect backing format for readonly drive overlays (RHBZ#1354335).

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If the user doesn't specify a format (ie. they want autodetection),
and the drive is set to read-only, previously we created a qcow2
overlay to protect the drive but didn't set the backing_fmt field.
However libvirt disabled this so now libvirt doesn't work at all on
qcow2 files that have no backing_fmt field set.

We must therefore do autodetection in libguestfs and use that to set
the backing_fmt field.

We were already doing autodetection in the non-readonly case, so this
commit refactors that code into a new function
("get_source_format_or_autodetect") and uses it on the readonly path
too.
This commit is contained in:
Richard W.M. Jones
2016-08-02 14:44:50 +01:00
parent 3b9cc56a45
commit c8c181e8d9
1 changed files with 66 additions and 34 deletions
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100
src/launch-libvirt.c
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@@ -162,6 +162,60 @@ static int check_bridge_exists (guestfs_h *g, const char *brname);
static void selinux_warning (guestfs_h *g, const char *func, const char *selinux_op, const char *data);
#endif
/**
* Return C<drv-E<gt>src.format>, but if it is C<NULL>, autodetect the
* format.
*
* libvirt has disabled the feature of detecting the disk format,
* unless the administrator sets C<allow_disk_format_probing=1> in
* F</etc/libvirt/qemu.conf>. There is no way to detect if this
* option is set, so we have to do format detection here using
* C<qemu-img> and pass that to libvirt.
*
* This can still be a security issue, so in most cases it is
* recommended the users pass the format to libguestfs which will
* faithfully pass that straight through to libvirt without doing
* autodetection.
*
* Caller must free the returned string. On error this function sets
* the error in the handle and returns C<NULL>.
*/
static char *
get_source_format_or_autodetect (guestfs_h *g, struct drive *drv)
{
if (drv->src.format)
return safe_strdup (g, drv->src.format);
if (drv->src.protocol == drive_protocol_file) {
char *format;
format = guestfs_disk_format (g, drv->src.u.path);
if (!format)
return NULL;
if (STREQ (format, "unknown")) {
error (g, _("could not auto-detect the format.\n"
"If the format is known, pass the format to libguestfs, eg. using the\n"
"'--format' option, or via the optional 'format' argument to 'add-drive'."));
return NULL;
}
return format;
}
/* Non-file protocol. */
error (g, _("could not auto-detect the format when using a non-file protocol.\n"
"If the format is known, pass the format to libguestfs, eg. using the\n"
"'--format' option, or via the optional 'format' argument to 'add-drive'."));
return NULL;
}
/**
* Create a qcow2 format overlay, with the given C<backing_drive>
* (file). The C<format> parameter, which must be non-NULL, is the
* backing file format. This is used to create the appliance overlay,
* and also for read-only drives.
*/
static char *
make_qcow2_overlay (guestfs_h *g, const char *backing_drive,
const char *format)
@@ -169,6 +223,8 @@ make_qcow2_overlay (guestfs_h *g, const char *backing_drive,
char *overlay;
struct guestfs_disk_create_argv optargs;
assert (format != NULL);
if (guestfs_int_lazy_make_tmpdir (g) == -1)
return NULL;
@@ -176,10 +232,8 @@ make_qcow2_overlay (guestfs_h *g, const char *backing_drive,
optargs.bitmask = GUESTFS_DISK_CREATE_BACKINGFILE_BITMASK;
optargs.backingfile = backing_drive;
if (format) {
optargs.bitmask |= GUESTFS_DISK_CREATE_BACKINGFORMAT_BITMASK;
optargs.backingformat = format;
}
optargs.bitmask |= GUESTFS_DISK_CREATE_BACKINGFORMAT_BITMASK;
optargs.backingformat = format;
if (guestfs_disk_create_argv (g, overlay, "qcow2", -1, &optargs) == -1) {
free (overlay);
@@ -196,13 +250,18 @@ create_cow_overlay_libvirt (guestfs_h *g, void *datav, struct drive *drv)
struct backend_libvirt_data *data = datav;
#endif
CLEANUP_FREE char *backing_drive = NULL;
CLEANUP_FREE char *format = NULL;
char *overlay;
backing_drive = guestfs_int_drive_source_qemu_param (g, &drv->src);
if (!backing_drive)
return NULL;
overlay = make_qcow2_overlay (g, backing_drive, drv->src.format);
format = get_source_format_or_autodetect (g, drv);
if (!format)
return NULL;
overlay = make_qcow2_overlay (g, backing_drive, format);
if (!overlay)
return NULL;
@@ -1480,36 +1539,9 @@ construct_libvirt_xml_disk (guestfs_h *g,
if (construct_libvirt_xml_disk_target (g, xo, drv_index) == -1)
return -1;
if (drv->src.format)
format = safe_strdup (g, drv->src.format);
else if (drv->src.protocol == drive_protocol_file) {
/* libvirt has disabled the feature of detecting the disk format,
* unless the administrator sets allow_disk_format_probing=1 in
* qemu.conf. There is no way to detect if this option is set, so we
* have to do format detection here using qemu-img and pass that to
* libvirt.
*
* This is still a security issue, so in most cases it is recommended
* the users pass the format to libguestfs which will faithfully pass
* that to libvirt and this function won't be used.
*/
format = guestfs_disk_format (g, drv->src.u.path);
if (!format)
return -1;
if (STREQ (format, "unknown")) {
error (g, _("could not auto-detect the format.\n"
"If the format is known, pass the format to libguestfs, eg. using the\n"
"'--format' option, or via the optional 'format' argument to 'add-drive'."));
return -1;
}
}
else {
error (g, _("could not auto-detect the format when using a non-file protocol.\n"
"If the format is known, pass the format to libguestfs, eg. using the\n"
"'--format' option, or via the optional 'format' argument to 'add-drive'."));
format = get_source_format_or_autodetect (g, drv);
if (!format)
return -1;
}
if (construct_libvirt_xml_disk_driver_qemu (g, data, drv, xo, format,
drv->cachemode ? : "writeback",