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vmspawn-qmp: derive QMP node and device ids from a bridge counter

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Replace the caller-supplied DriveInfo.node_name with two QMP-internal
strings generated at setup time from a monotonic per-bridge counter:

  qmp_node_name   = "vmspawn-<N>-storage"  (blockdev node-name)
  qmp_device_id   = "vmspawn-<N>-disk"     (qdev id)

This is the naming scheme the upcoming runtime-hotplug add path needs:
unique across the lifetime of the VM, decoupled from any user-visible id,
and stable across the four QMP commands that make up an add (add-fd,
blockdev-add, remove-fd, device_add). The boot-time setups don't care
about uniqueness, but switching them now means the hotplug path can share
qmp_build_device_add() and EphemeralDriveCtx without a parallel naming
scheme.

vmspawn.c stops assigning node_name in prepare_primary_drive (which used
the literal "vmspawn") and prepare_extra_drives (which counted
"vmspawn_extra_%zu"); both are replaced by the bridge counter at the
point the drive is actually pushed into QEMU. Ephemeral helper-node
names follow the same vmspawn-<N>-{base-file,base-fmt,overlay-file}
convention; the blockdev-create job-id becomes
vmspawn-<N>-overlay-create.

EphemeralDriveCtx grows a qmp_device_id field (the qdev id is
independent of the format node-name now) and renames node_name →
qmp_node_name to match. No external behaviour change other than the new
internal names.

Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
This commit is contained in:
Christian Brauner
2026-04-24 14:39:25 +02:00
parent f0c1dc50ef
commit a57fbf4e6c
3 changed files with 53 additions and 48 deletions
Download Patch File Download Diff File Expand all files Collapse all files
src/vmspawn/vmspawn-qmp.c
+48 -40
View File
@@ -45,7 +45,8 @@ static DriveInfo* drive_info_free(DriveInfo *d) {
free(d->format);
free(d->disk_driver);
free(d->serial);
free(d->node_name);
free(d->qmp_node_name);
free(d->qmp_device_id);
free(d->pcie_port);
safe_close(d->fd);
safe_close(d->overlay_fd);
@@ -213,16 +214,17 @@ static int qmp_build_blockdev_add_format(const QmpFormatNodeParams *p, sd_json_v
SD_JSON_BUILD_PAIR_CONDITION(!!p->backing, "backing", SD_JSON_BUILD_STRING(p->backing)));
}
/* Build device_add JSON arguments for a drive */
static int qmp_build_device_add(const DriveInfo *drive, sd_json_variant **ret) {
assert(drive);
assert(drive->qmp_node_name);
assert(drive->qmp_device_id);
assert(ret);
return sd_json_buildo(
ret,
SD_JSON_BUILD_PAIR_STRING("driver", drive->disk_driver),
SD_JSON_BUILD_PAIR_STRING("drive", drive->node_name),
SD_JSON_BUILD_PAIR_STRING("id", drive->node_name),
SD_JSON_BUILD_PAIR_STRING("drive", drive->qmp_node_name),
SD_JSON_BUILD_PAIR_STRING("id", drive->qmp_device_id),
SD_JSON_BUILD_PAIR_CONDITION(FLAGS_SET(drive->flags, QMP_DRIVE_BOOT), "bootindex", SD_JSON_BUILD_INTEGER(1)),
SD_JSON_BUILD_PAIR_CONDITION(!!drive->serial, "serial", SD_JSON_BUILD_STRING(drive->serial)),
SD_JSON_BUILD_PAIR_CONDITION(STR_IN_SET(drive->disk_driver, "scsi-hd", "scsi-cd"),
@@ -292,23 +294,23 @@ static int get_image_virtual_size(int fd, const char *format, bool is_block_devi
return log_error_errno(SYNTHETIC_ERRNO(EOPNOTSUPP), "Unsupported image format '%s'", format);
}
/* Ephemeral drive continuation — fired when the blockdev-create job concludes.
* Completes the drive setup by adding the overlay format node and the device. */
/* Continuation state for on_ephemeral_create_concluded: overlay format + device_add. */
typedef struct EphemeralDriveCtx {
char *node_name; /* overlay format node name (= drive node name) */
char *qmp_node_name; /* overlay format node name, "vmspawn-<N>-storage" */
char *qmp_device_id; /* qdev id, "vmspawn-<N>-disk" */
char *overlay_file_node;
char *base_fmt_node;
/* Fields for device_add */
char *disk_driver;
char *serial; /* NULL if unset */
char *pcie_port; /* pcie-root-port bus for device_add (NULL on non-PCIe) */
QmpDriveFlags flags; /* subset: QMP_DRIVE_DISCARD, QMP_DRIVE_DISCARD_NO_UNREF, QMP_DRIVE_BOOT */
char *serial;
char *pcie_port; /* NULL on non-PCIe */
QmpDriveFlags flags; /* subset forwarded to device_add */
} EphemeralDriveCtx;
static EphemeralDriveCtx* ephemeral_drive_ctx_free(EphemeralDriveCtx *ctx) {
if (!ctx)
return NULL;
free(ctx->node_name);
free(ctx->qmp_node_name);
free(ctx->qmp_device_id);
free(ctx->overlay_file_node);
free(ctx->base_fmt_node);
free(ctx->disk_driver);
@@ -330,7 +332,7 @@ static int on_ephemeral_create_concluded(QmpClient *qmp, void *userdata) {
/* Open formatted overlay as qcow2 with backing reference */
QmpFormatNodeParams overlay_fmt_params = {
.node_name = ctx->node_name,
.node_name = ctx->qmp_node_name,
.format = "qcow2",
.file_node_name = ctx->overlay_file_node,
.backing = ctx->base_fmt_node,
@@ -338,32 +340,32 @@ static int on_ephemeral_create_concluded(QmpClient *qmp, void *userdata) {
};
r = qmp_build_blockdev_add_format(&overlay_fmt_params, &fmt_args);
if (r < 0)
return log_error_errno(r, "Failed to build overlay format JSON for '%s': %m", ctx->node_name);
return log_error_errno(r, "Failed to build overlay format JSON for '%s': %m", ctx->qmp_node_name);
r = qmp_client_invoke(qmp, /* ret_slot= */ NULL, "blockdev-add", QMP_CLIENT_ARGS(fmt_args), on_qmp_complete, (void*) "blockdev-add");
if (r < 0)
return r;
/* device_add: attach to virtual hardware. Build a temporary DriveInfo as a
* read-only view into the continuation context to reuse qmp_build_device_add(). */
/* Temporary DriveInfo view so we can reuse qmp_build_device_add(). */
const DriveInfo tmp = {
.disk_driver = ctx->disk_driver,
.node_name = ctx->node_name,
.serial = ctx->serial,
.pcie_port = ctx->pcie_port,
.flags = ctx->flags & QMP_DRIVE_BOOT,
.fd = -EBADF,
.overlay_fd = -EBADF,
.disk_driver = ctx->disk_driver,
.serial = ctx->serial,
.pcie_port = ctx->pcie_port,
.flags = ctx->flags & QMP_DRIVE_BOOT,
.fd = -EBADF,
.overlay_fd = -EBADF,
.qmp_node_name = ctx->qmp_node_name,
.qmp_device_id = ctx->qmp_device_id,
};
r = qmp_build_device_add(&tmp, &device_args);
if (r < 0)
return log_error_errno(r, "Failed to build device_add JSON for '%s': %m", ctx->node_name);
return log_error_errno(r, "Failed to build device_add JSON for '%s': %m", ctx->qmp_device_id);
r = qmp_client_invoke(qmp, /* ret_slot= */ NULL, "device_add", QMP_CLIENT_ARGS(device_args), on_qmp_complete, (void*) "device_add");
if (r < 0)
return r;
log_debug("Queued ephemeral drive completion for '%s'", ctx->node_name);
log_debug("Queued ephemeral drive completion for '%s'", ctx->qmp_device_id);
return 0;
}
@@ -379,11 +381,14 @@ static int qmp_setup_ephemeral_drive(VmspawnQmpBridge *bridge, QmpClient *qmp, D
assert(drive->fd >= 0);
assert(drive->overlay_fd >= 0);
/* Node names: <name>-base-file, <name>-base-fmt, <name>-overlay-file, <name> */
_cleanup_free_ char *base_file_node = strjoin(drive->node_name, "-base-file");
_cleanup_free_ char *base_fmt_node = strjoin(drive->node_name, "-base-fmt");
_cleanup_free_ char *overlay_file_node = strjoin(drive->node_name, "-overlay-file");
if (!base_file_node || !base_fmt_node || !overlay_file_node)
uint64_t counter = bridge->next_block_counter++;
_cleanup_free_ char *base_file_node = NULL, *base_fmt_node = NULL, *overlay_file_node = NULL;
if (asprintf(&drive->qmp_node_name, "vmspawn-%" PRIu64 "-storage", counter) < 0 ||
asprintf(&drive->qmp_device_id, "vmspawn-%" PRIu64 "-disk", counter) < 0 ||
asprintf(&base_file_node, "vmspawn-%" PRIu64 "-base-file", counter) < 0 ||
asprintf(&base_fmt_node, "vmspawn-%" PRIu64 "-base-fmt", counter) < 0 ||
asprintf(&overlay_file_node, "vmspawn-%" PRIu64 "-overlay-file", counter) < 0)
return log_oom();
/* Read virtual size before passing the fd to QEMU (TAKE_FD consumes it) */
@@ -459,8 +464,8 @@ static int qmp_setup_ephemeral_drive(VmspawnQmpBridge *bridge, QmpClient *qmp, D
if (r < 0)
return log_error_errno(r, "Failed to build blockdev-create options: %m");
_cleanup_free_ char *job_id = strjoin("create-", drive->node_name);
if (!job_id)
_cleanup_free_ char *job_id = NULL;
if (asprintf(&job_id, "vmspawn-%" PRIu64 "-overlay-create", counter) < 0)
return log_oom();
_cleanup_(sd_json_variant_unrefp) sd_json_variant *cmd_args = NULL;
@@ -481,7 +486,8 @@ static int qmp_setup_ephemeral_drive(VmspawnQmpBridge *bridge, QmpClient *qmp, D
ectx_flags |= QMP_DRIVE_DISCARD_NO_UNREF;
*ectx = (EphemeralDriveCtx) {
.node_name = strdup(drive->node_name),
.qmp_node_name = strdup(drive->qmp_node_name),
.qmp_device_id = strdup(drive->qmp_device_id),
.overlay_file_node = strdup(overlay_file_node),
.base_fmt_node = strdup(base_fmt_node),
.disk_driver = strdup(drive->disk_driver),
@@ -489,9 +495,9 @@ static int qmp_setup_ephemeral_drive(VmspawnQmpBridge *bridge, QmpClient *qmp, D
.pcie_port = drive->pcie_port ? strdup(drive->pcie_port) : NULL,
.flags = ectx_flags,
};
if (!ectx->node_name || !ectx->overlay_file_node || !ectx->base_fmt_node ||
!ectx->disk_driver || (drive->serial && !ectx->serial) ||
(drive->pcie_port && !ectx->pcie_port))
if (!ectx->qmp_node_name || !ectx->qmp_device_id || !ectx->overlay_file_node ||
!ectx->base_fmt_node || !ectx->disk_driver ||
(drive->serial && !ectx->serial) || (drive->pcie_port && !ectx->pcie_port))
return log_oom();
r = vmspawn_qmp_bridge_register_job(bridge, job_id,
@@ -519,9 +525,11 @@ static int qmp_setup_regular_drive(VmspawnQmpBridge *bridge, QmpClient *qmp, Dri
assert(drive);
assert(drive->fd >= 0);
/* Node names: <name>-file, <name> */
_cleanup_free_ char *file_node_name = strjoin(drive->node_name, "-file");
if (!file_node_name)
uint64_t counter = bridge->next_block_counter++;
_cleanup_free_ char *file_node_name = NULL;
if (asprintf(&drive->qmp_node_name, "vmspawn-%" PRIu64 "-storage", counter) < 0 ||
asprintf(&drive->qmp_device_id, "vmspawn-%" PRIu64 "-disk", counter) < 0 ||
asprintf(&file_node_name, "vmspawn-%" PRIu64 "-file", counter) < 0)
return log_oom();
_cleanup_free_ char *fdset_path = NULL;
@@ -542,7 +550,7 @@ static int qmp_setup_regular_drive(VmspawnQmpBridge *bridge, QmpClient *qmp, Dri
return log_error_errno(r, "Failed to send blockdev-add for '%s': %m", drive->path);
QmpFormatNodeParams fmt_params = {
.node_name = drive->node_name,
.node_name = drive->qmp_node_name,
.format = drive->format,
.file_node_name = file_node_name,
.flags = drive->flags & (QMP_DRIVE_READ_ONLY|QMP_DRIVE_DISCARD),
src/vmspawn/vmspawn-qmp.h
+4 -2
View File
@@ -28,7 +28,8 @@ typedef enum VmspawnQmpFeatureFlags {
typedef struct VmspawnQmpBridge {
QmpClient *qmp;
Hashmap *pending_jobs; /* job_id (string, owned) -> PendingJob* */
Hashmap *pending_jobs; /* blockdev-create continuations */
uint64_t next_block_counter; /* monotonic counter feeding internal QMP names (vmspawn-<N>-*) */
VmspawnQmpFeatureFlags features;
bool setup_done;
} VmspawnQmpBridge;
@@ -76,7 +77,8 @@ typedef struct DriveInfo {
char *format; /* "raw" or "qcow2" */
char *disk_driver; /* "virtio-blk-pci", "scsi-hd", "scsi-cd", "nvme" */
char *serial;
char *node_name;
char *qmp_node_name; /* "vmspawn-<N>-storage" */
char *qmp_device_id; /* "vmspawn-<N>-disk" */
char *pcie_port; /* pcie-root-port id for device_add bus (NULL on non-PCIe) */
int fd; /* pre-opened image fd (-EBADF if unused) */
int overlay_fd; /* pre-opened anonymous overlay fd for ephemeral (-EBADF if unused) */
src/vmspawn/vmspawn.c
+1 -6
View File
@@ -2343,8 +2343,7 @@ static int prepare_primary_drive(const char *runtime_dir, DriveInfos *drives) {
d->path = strdup(arg_image);
d->format = strdup(ASSERT_PTR(image_format_to_string(arg_image_format)));
d->node_name = strdup("vmspawn");
if (!d->path || !d->format || !d->node_name)
if (!d->path || !d->format)
return log_oom();
d->fd = TAKE_FD(image_fd);
if (S_ISBLK(st.st_mode))
@@ -2380,7 +2379,6 @@ static int prepare_extra_drives(DriveInfos *drives) {
assert(drives);
size_t extra_idx = 0;
FOREACH_ARRAY(drive, arg_extra_drives.drives, arg_extra_drives.n_drives) {
_cleanup_free_ char *drive_fn = NULL;
r = path_extract_filename(drive->path, &drive_fn);
@@ -2421,9 +2419,6 @@ static int prepare_extra_drives(DriveInfos *drives) {
d->flags |= QMP_DRIVE_BLOCK_DEVICE;
d->flags |= QMP_DRIVE_NO_FLUSH;
if (asprintf(&d->node_name, "vmspawn_extra_%zu", extra_idx++) < 0)
return log_oom();
drives->drives[drives->n_drives++] = TAKE_PTR(d);
}