[Libguestfs] [PATCH v4 2/5] launch: libvirt: Create qcow2 overlays for read-only drives and the appliance.
Richard W.M. Jones
rjones at redhat.com
Mon Oct 8 19:05:51 UTC 2012
From: "Richard W.M. Jones" <rjones at redhat.com>
Instead of adding the snapshot=on option via <qemu:arg>, create qcow2
overlays for any read-only drives and the appliance using 'qemu-img
create' + a temporary file.
This is a workaround for missing support for <transient/> in libvirt's
qemu driver. Also for the unpredictable way that libvirtd handles
$TMPDIR: we want to control where the temporary disk is created.
Currently it is also much slower, because qemu-img is slow. However
we hope to fix qemu upstream.
---
src/launch-libvirt.c | 298 +++++++++++++++++++++++++++++++++++++-------------
1 file changed, 219 insertions(+), 79 deletions(-)
diff --git a/src/launch-libvirt.c b/src/launch-libvirt.c
index 7ae37e3..d33693e 100644
--- a/src/launch-libvirt.c
+++ b/src/launch-libvirt.c
@@ -28,6 +28,7 @@
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/wait.h>
+#include <assert.h>
#ifdef HAVE_LIBVIRT
#include <libvirt/libvirt.h>
@@ -92,12 +93,26 @@ xmlBufferDetach (xmlBufferPtr buf)
}
#endif
-static xmlChar *construct_libvirt_xml (guestfs_h *g, const char *capabilities_xml, const char *kernel, const char *initrd, const char *appliance, const char *guestfsd_sock, const char *console_sock, int disable_svirt);
+/* Pointed to by 'struct drive *' -> priv field. */
+struct drive_libvirt {
+ /* This is either the original path, made absolute. Or for readonly
+ * drives, it is an (absolute path to) the overlay file that we
+ * create. This is always non-NULL.
+ */
+ char *path;
+ /* The format of priv->path. */
+ char *format;
+};
+
+static xmlChar *construct_libvirt_xml (guestfs_h *g, const char *capabilities_xml, const char *kernel, const char *initrd, const char *appliance_overlay, const char *guestfsd_sock, const char *console_sock, int disable_svirt);
static void libvirt_error (guestfs_h *g, const char *fs, ...);
static int is_custom_qemu (guestfs_h *g);
static int is_blk (const char *path);
static int random_chars (char *ret, size_t len);
static void ignore_errors (void *ignore, virErrorPtr ignore2);
+static char *make_qcow2_overlay (guestfs_h *g, const char *path, const char *format);
+static int make_qcow2_overlay_for_drive (guestfs_h *g, struct drive *drv);
+static void drive_free_priv (void *);
static int
launch_libvirt (guestfs_h *g, const char *libvirt_uri)
@@ -109,6 +124,7 @@ launch_libvirt (guestfs_h *g, const char *libvirt_uri)
char *capabilities = NULL;
xmlChar *xml = NULL;
char *kernel = NULL, *initrd = NULL, *appliance = NULL;
+ char *appliance_overlay = NULL;
char guestfsd_sock[256];
char console_sock[256];
struct sockaddr_un addr;
@@ -116,6 +132,8 @@ launch_libvirt (guestfs_h *g, const char *libvirt_uri)
uint32_t size;
void *buf = NULL;
int disable_svirt = is_custom_qemu (g);
+ struct drive *drv;
+ size_t i;
/* At present you must add drives before starting the appliance. In
* future when we enable hotplugging you won't need to do this.
@@ -182,6 +200,20 @@ launch_libvirt (guestfs_h *g, const char *libvirt_uri)
guestfs___launch_send_progress (g, 3);
TRACE0 (launch_build_libvirt_appliance_end);
+ /* Create overlays for read-only drives and the appliance. This
+ * works around lack of support for <transient/> disks in libvirt.
+ */
+ appliance_overlay = make_qcow2_overlay (g, appliance, "raw");
+ if (!appliance_overlay)
+ goto cleanup;
+
+ ITER_DRIVES (g, i, drv) {
+ if (make_qcow2_overlay_for_drive (g, drv) == -1)
+ goto cleanup;
+ }
+
+ TRACE0 (launch_build_libvirt_qcow2_overlay_end);
+
/* Using virtio-serial, we need to create a local Unix domain socket
* for qemu to connect to.
*/
@@ -278,7 +310,7 @@ launch_libvirt (guestfs_h *g, const char *libvirt_uri)
guestfs___print_timestamped_message (g, "create libvirt XML");
xml = construct_libvirt_xml (g, capabilities,
- kernel, initrd, appliance,
+ kernel, initrd, appliance_overlay,
guestfsd_sock, console_sock,
disable_svirt);
if (!xml)
@@ -381,6 +413,7 @@ launch_libvirt (guestfs_h *g, const char *libvirt_uri)
free (kernel);
free (initrd);
free (appliance);
+ free (appliance_overlay);
free (xml);
free (capabilities);
@@ -412,6 +445,7 @@ launch_libvirt (guestfs_h *g, const char *libvirt_uri)
free (kernel);
free (initrd);
free (appliance);
+ free (appliance_overlay);
free (capabilities);
free (xml);
@@ -431,10 +465,10 @@ static int construct_libvirt_xml_cpu (guestfs_h *g, xmlTextWriterPtr xo);
static int construct_libvirt_xml_boot (guestfs_h *g, xmlTextWriterPtr xo, const char *kernel, const char *initrd, size_t appliance_index);
static int construct_libvirt_xml_seclabel (guestfs_h *g, xmlTextWriterPtr xo);
static int construct_libvirt_xml_lifecycle (guestfs_h *g, xmlTextWriterPtr xo);
-static int construct_libvirt_xml_devices (guestfs_h *g, xmlTextWriterPtr xo, const char *appliance, size_t appliance_index, const char *guestfsd_sock, const char *console_sock);
+static int construct_libvirt_xml_devices (guestfs_h *g, xmlTextWriterPtr xo, const char *appliance_overlay, size_t appliance_index, const char *guestfsd_sock, const char *console_sock);
static int construct_libvirt_xml_qemu_cmdline (guestfs_h *g, xmlTextWriterPtr xo);
static int construct_libvirt_xml_disk (guestfs_h *g, xmlTextWriterPtr xo, struct drive *drv, size_t drv_index);
-static int construct_libvirt_xml_appliance (guestfs_h *g, xmlTextWriterPtr xo, const char *appliance, size_t appliance_index);
+static int construct_libvirt_xml_appliance (guestfs_h *g, xmlTextWriterPtr xo, const char *appliance_overlay, size_t appliance_index);
#define XMLERROR(code,e) do { \
if ((e) == (code)) { \
@@ -447,7 +481,7 @@ static int construct_libvirt_xml_appliance (guestfs_h *g, xmlTextWriterPtr xo, c
static xmlChar *
construct_libvirt_xml (guestfs_h *g, const char *capabilities_xml,
const char *kernel, const char *initrd,
- const char *appliance,
+ const char *appliance_overlay,
const char *guestfsd_sock, const char *console_sock,
int disable_svirt)
{
@@ -490,7 +524,7 @@ construct_libvirt_xml (guestfs_h *g, const char *capabilities_xml,
goto err;
if (construct_libvirt_xml_lifecycle (g, xo) == -1)
goto err;
- if (construct_libvirt_xml_devices (g, xo, appliance, appliance_index,
+ if (construct_libvirt_xml_devices (g, xo, appliance_overlay, appliance_index,
guestfsd_sock, console_sock) == -1)
goto err;
if (construct_libvirt_xml_qemu_cmdline (g, xo) == -1)
@@ -675,7 +709,8 @@ construct_libvirt_xml_lifecycle (guestfs_h *g, xmlTextWriterPtr xo)
/* Devices. */
static int
construct_libvirt_xml_devices (guestfs_h *g, xmlTextWriterPtr xo,
- const char *appliance, size_t appliance_index,
+ const char *appliance_overlay,
+ size_t appliance_index,
const char *guestfsd_sock,
const char *console_sock)
{
@@ -713,7 +748,8 @@ construct_libvirt_xml_devices (guestfs_h *g, xmlTextWriterPtr xo,
}
/* Appliance disk. */
- if (construct_libvirt_xml_appliance (g, xo, appliance, appliance_index) == -1)
+ if (construct_libvirt_xml_appliance (g, xo, appliance_overlay,
+ appliance_index) == -1)
goto err;
/* Console. */
@@ -773,7 +809,7 @@ construct_libvirt_xml_disk (guestfs_h *g, xmlTextWriterPtr xo,
{
char drive_name[64] = "sd";
char scsi_target[64];
- char *path = NULL;
+ struct drive_libvirt *drv_priv;
char *format = NULL;
int is_host_device;
@@ -786,6 +822,8 @@ construct_libvirt_xml_disk (guestfs_h *g, xmlTextWriterPtr xo,
guestfs___drive_name (drv_index, &drive_name[2]);
snprintf (scsi_target, sizeof scsi_target, "%zu", drv_index);
+ drv_priv = (struct drive_libvirt *) drv->priv;
+
/* Change the libvirt XML according to whether the host path is
* a device or a file. For devices, use:
* <disk type=block device=disk>
@@ -794,15 +832,7 @@ construct_libvirt_xml_disk (guestfs_h *g, xmlTextWriterPtr xo,
* <disk type=file device=disk>
* <source file=[path]>
*/
- is_host_device = is_blk (drv->path);
-
- /* Path must be absolute for libvirt. */
- path = realpath (drv->path, NULL);
- if (path == NULL) {
- perrorf (g, _("realpath: could not convert '%s' to absolute path"),
- drv->path);
- goto err;
- }
+ is_host_device = is_blk (drv_priv->path);
XMLERROR (-1, xmlTextWriterStartElement (xo, BAD_CAST "disk"));
XMLERROR (-1,
@@ -815,7 +845,8 @@ construct_libvirt_xml_disk (guestfs_h *g, xmlTextWriterPtr xo,
XMLERROR (-1, xmlTextWriterStartElement (xo, BAD_CAST "source"));
XMLERROR (-1,
- xmlTextWriterWriteAttribute (xo, BAD_CAST "file", BAD_CAST path));
+ xmlTextWriterWriteAttribute (xo, BAD_CAST "file",
+ BAD_CAST drv_priv->path));
XMLERROR (-1, xmlTextWriterEndElement (xo));
}
else {
@@ -825,7 +856,8 @@ construct_libvirt_xml_disk (guestfs_h *g, xmlTextWriterPtr xo,
XMLERROR (-1, xmlTextWriterStartElement (xo, BAD_CAST "source"));
XMLERROR (-1,
- xmlTextWriterWriteAttribute (xo, BAD_CAST "dev", BAD_CAST path));
+ xmlTextWriterWriteAttribute (xo, BAD_CAST "dev",
+ BAD_CAST drv_priv->path));
XMLERROR (-1, xmlTextWriterEndElement (xo));
}
@@ -842,10 +874,10 @@ construct_libvirt_xml_disk (guestfs_h *g, xmlTextWriterPtr xo,
XMLERROR (-1,
xmlTextWriterWriteAttribute (xo, BAD_CAST "name",
BAD_CAST "qemu"));
- if (drv->format) {
+ if (drv_priv->format) {
XMLERROR (-1,
xmlTextWriterWriteAttribute (xo, BAD_CAST "type",
- BAD_CAST drv->format));
+ BAD_CAST drv_priv->format));
}
else {
/* libvirt has disabled the feature of detecting the disk format,
@@ -858,7 +890,7 @@ construct_libvirt_xml_disk (guestfs_h *g, xmlTextWriterPtr xo,
* 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, path);
+ format = guestfs_disk_format (g, drv_priv->path);
if (!format)
goto err;
@@ -866,7 +898,7 @@ construct_libvirt_xml_disk (guestfs_h *g, xmlTextWriterPtr xo,
error (g, _("could not auto-detect the format of '%s'\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'."),
- path);
+ drv->path);
goto err;
}
@@ -899,30 +931,20 @@ construct_libvirt_xml_disk (guestfs_h *g, xmlTextWriterPtr xo,
BAD_CAST "0"));
XMLERROR (-1, xmlTextWriterEndElement (xo));
- /* We'd like to do this, but it's not supported by libvirt.
- * See construct_libvirt_xml_qemu_cmdline for the workaround.
- *
- * if (drv->readonly) {
- * XMLERROR (-1, xmlTextWriterStartElement (xo, BAD_CAST "transient"));
- * XMLERROR (-1, xmlTextWriterEndElement (xo));
- * }
- */
-
XMLERROR (-1, xmlTextWriterEndElement (xo));
- free (path);
free (format);
return 0;
err:
- free (path);
free (format);
return -1;
}
static int
construct_libvirt_xml_appliance (guestfs_h *g, xmlTextWriterPtr xo,
- const char *appliance, size_t drv_index)
+ const char *appliance_overlay,
+ size_t drv_index)
{
char drive_name[64] = "sd";
char scsi_target[64];
@@ -941,7 +963,7 @@ construct_libvirt_xml_appliance (guestfs_h *g, xmlTextWriterPtr xo,
XMLERROR (-1, xmlTextWriterStartElement (xo, BAD_CAST "source"));
XMLERROR (-1,
xmlTextWriterWriteAttribute (xo, BAD_CAST "file",
- BAD_CAST appliance));
+ BAD_CAST appliance_overlay));
XMLERROR (-1, xmlTextWriterEndElement (xo));
XMLERROR (-1, xmlTextWriterStartElement (xo, BAD_CAST "target"));
@@ -959,7 +981,7 @@ construct_libvirt_xml_appliance (guestfs_h *g, xmlTextWriterPtr xo,
BAD_CAST "qemu"));
XMLERROR (-1,
xmlTextWriterWriteAttribute (xo, BAD_CAST "type",
- BAD_CAST "raw"));
+ BAD_CAST "qcow2"));
XMLERROR (-1,
xmlTextWriterWriteAttribute (xo, BAD_CAST "cache",
BAD_CAST "unsafe"));
@@ -1004,52 +1026,11 @@ construct_libvirt_xml_appliance (guestfs_h *g, xmlTextWriterPtr xo,
static int
construct_libvirt_xml_qemu_cmdline (guestfs_h *g, xmlTextWriterPtr xo)
{
- struct drive *drv;
- size_t i;
- char attr[256];
struct qemu_param *qp;
char *p;
XMLERROR (-1, xmlTextWriterStartElement (xo, BAD_CAST "qemu:commandline"));
- /* Workaround because libvirt can't do snapshot=on yet. Idea inspired
- * by Stefan Hajnoczi's post here:
- * http://blog.vmsplice.net/2011/04/how-to-pass-qemu-command-line-options.html
- */
- ITER_DRIVES (g, i, drv) {
- if (drv->readonly) {
- snprintf (attr, sizeof attr,
- "drive.drive-scsi0-0-%zu-0.snapshot=on", i);
-
- XMLERROR (-1, xmlTextWriterStartElement (xo, BAD_CAST "qemu:arg"));
- XMLERROR (-1,
- xmlTextWriterWriteAttribute (xo, BAD_CAST "value",
- BAD_CAST "-set"));
- XMLERROR (-1, xmlTextWriterEndElement (xo));
-
- XMLERROR (-1, xmlTextWriterStartElement (xo, BAD_CAST "qemu:arg"));
- XMLERROR (-1,
- xmlTextWriterWriteAttribute (xo, BAD_CAST "value",
- BAD_CAST attr));
- XMLERROR (-1, xmlTextWriterEndElement (xo));
- }
- }
-
- snprintf (attr, sizeof attr,
- "drive.drive-scsi0-0-%zu-0.snapshot=on", g->nr_drives);
-
- XMLERROR (-1, xmlTextWriterStartElement (xo, BAD_CAST "qemu:arg"));
- XMLERROR (-1,
- xmlTextWriterWriteAttribute (xo, BAD_CAST "value",
- BAD_CAST "-set"));
- XMLERROR (-1, xmlTextWriterEndElement (xo));
-
- XMLERROR (-1, xmlTextWriterStartElement (xo, BAD_CAST "qemu:arg"));
- XMLERROR (-1,
- xmlTextWriterWriteAttribute (xo, BAD_CAST "value",
- BAD_CAST attr));
- XMLERROR (-1, xmlTextWriterEndElement (xo));
-
/* We need to ensure the snapshots are created in $TMPDIR (RHBZ#856619). */
p = getenv ("TMPDIR");
if (p) {
@@ -1162,6 +1143,165 @@ ignore_errors (void *ignore, virErrorPtr ignore2)
/* empty */
}
+/* Create a temporary qcow2 overlay on top of 'path'. */
+static char *
+make_qcow2_overlay (guestfs_h *g, const char *path, const char *format)
+{
+ char *tmpfile = NULL;
+ int fd[2] = { -1, -1 };
+ pid_t pid = -1;
+ FILE *fp = NULL;
+ char *line = NULL;
+ size_t len;
+ int r;
+
+ /* Path must be absolute. */
+ assert (path);
+ assert (path[0] == '/');
+
+ tmpfile = safe_asprintf (g, "%s/snapshot%d", g->tmpdir, ++g->unique);
+
+ /* Because 'qemu-img create' spews junk to stdout and stderr, pass
+ * all output from it up through the event system.
+ * XXX Like libvirt, we should create a generic library for running
+ * commands.
+ */
+ if (pipe2 (fd, O_CLOEXEC) == -1) {
+ perrorf (g, "pipe2");
+ goto error;
+ }
+
+ pid = fork ();
+ if (pid == -1) {
+ perrorf (g, "fork");
+ goto error;
+ }
+
+ if (pid == 0) { /* child: qemu-img create command */
+ /* Capture stdout and stderr. */
+ close (fd[0]);
+ dup2 (fd[1], 1);
+ dup2 (fd[1], 2);
+ close (fd[1]);
+
+ setenv ("LC_ALL", "C", 1);
+
+ if (!format)
+ execlp ("qemu-img", "qemu-img", "create", "-f", "qcow2",
+ "-b", path, tmpfile, NULL);
+ else {
+ size_t len = strlen (format);
+ char backing_fmt[len+64];
+
+ snprintf (backing_fmt, len+64, "backing_fmt=%s", format);
+
+ execlp ("qemu-img", "qemu-img", "create", "-f", "qcow2",
+ "-b", path, "-o", backing_fmt, tmpfile, NULL);
+ }
+
+ perror ("could not execute 'qemu-img create' command");
+ _exit (EXIT_FAILURE);
+ }
+
+ close (fd[1]);
+ fd[1] = -1;
+
+ fp = fdopen (fd[0], "r");
+ if (fp == NULL) {
+ perrorf (g, "fdopen: qemu-img create");
+ goto error;
+ }
+ fd[0] = -1;
+
+ while (getline (&line, &len, fp) != -1) {
+ guestfs___call_callbacks_message (g, GUESTFS_EVENT_LIBRARY, line, len);
+ }
+
+ if (fclose (fp) == -1) { /* also closes fd[0] */
+ perrorf (g, "fclose");
+ fp = NULL;
+ goto error;
+ }
+ fp = NULL;
+
+ free (line);
+ line = NULL;
+
+ if (waitpid (pid, &r, 0) == -1) {
+ perrorf (g, "waitpid");
+ pid = 0;
+ goto error;
+ }
+ pid = 0;
+
+ if (!WIFEXITED (r) || WEXITSTATUS (r) != 0) {
+ error (g, _("qemu-img create: could not create snapshot over %s"), path);
+ goto error;
+ }
+
+ return tmpfile; /* caller frees */
+
+ error:
+ if (fd[0] >= 0)
+ close (fd[0]);
+ if (fd[1] >= 0)
+ close (fd[1]);
+ if (fp != NULL)
+ fclose (fp);
+ if (pid > 0)
+ waitpid (pid, NULL, 0);
+
+ free (tmpfile);
+ free (line);
+
+ return NULL;
+}
+
+static int
+make_qcow2_overlay_for_drive (guestfs_h *g, struct drive *drv)
+{
+ char *path;
+ struct drive_libvirt *drv_priv;
+
+ if (drv->priv && drv->free_priv)
+ drv->free_priv (drv->priv);
+
+ drv->priv = drv_priv = safe_calloc (g, 1, sizeof (struct drive_libvirt));
+ drv->free_priv = drive_free_priv;
+
+ /* Even for non-readonly paths, we need to make the paths absolute here. */
+ path = realpath (drv->path, NULL);
+ if (path == NULL) {
+ perrorf (g, _("realpath: could not convert '%s' to absolute path"),
+ drv->path);
+ return -1;
+ }
+
+ if (!drv->readonly) {
+ drv_priv->path = path;
+ drv_priv->format = drv->format ? safe_strdup (g, drv->format) : NULL;
+ }
+ else {
+ drv_priv->path = make_qcow2_overlay (g, path, drv->format);
+ free (path);
+ if (!drv_priv->path)
+ return -1;
+ drv_priv->format = safe_strdup (g, "qcow2");
+ }
+
+ return 0;
+}
+
+static void
+drive_free_priv (void *priv)
+{
+ struct drive_libvirt *drv_priv = priv;
+
+ free (drv_priv->path);
+ free (drv_priv->format);
+ free (drv_priv);
+}
+
static int
shutdown_libvirt (guestfs_h *g, int check_for_errors)
{
--
1.7.10.4
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