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migration: per-mode blockers
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Extend the blocker interface so that a blocker can be registered for
one or more migration modes.  The existing interfaces register a
blocker for all modes, and the new interfaces take a varargs list
of modes.

Internally, maintain a separate blocker list per mode.  The same Error
object may be added to multiple lists.  When a block is deleted, it is
removed from every list, and the Error is freed.

No functional change until a new mode is added.

Signed-off-by: Steve Sistare <[email protected]>
Reviewed-by: Juan Quintela <[email protected]>
Signed-off-by: Juan Quintela <[email protected]>
Message-ID: <[email protected]>
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Steve Sistare authored and Juan Quintela committed Nov 1, 2023
1 parent eea1e5c commit fa3673e
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Showing 3 changed files with 132 additions and 17 deletions.
44 changes: 40 additions & 4 deletions include/migration/blocker.h
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Original file line number Diff line number Diff line change
Expand Up @@ -14,8 +14,12 @@
#ifndef MIGRATION_BLOCKER_H
#define MIGRATION_BLOCKER_H

#include "qapi/qapi-types-migration.h"

#define MIG_MODE_ALL MIG_MODE__MAX

/**
* @migrate_add_blocker - prevent migration from proceeding
* @migrate_add_blocker - prevent all modes of migration from proceeding
*
* @reasonp - address of an error to be returned whenever migration is attempted
*
Expand All @@ -30,8 +34,8 @@
int migrate_add_blocker(Error **reasonp, Error **errp);

/**
* @migrate_add_blocker_internal - prevent migration from proceeding without
* only-migrate implications
* @migrate_add_blocker_internal - prevent all modes of migration from
* proceeding, but ignore -only-migratable
*
* @reasonp - address of an error to be returned whenever migration is attempted
*
Expand All @@ -50,12 +54,44 @@ int migrate_add_blocker(Error **reasonp, Error **errp);
int migrate_add_blocker_internal(Error **reasonp, Error **errp);

/**
* @migrate_del_blocker - remove a blocking error from migration and free it.
* @migrate_del_blocker - remove a migration blocker from all modes and free it.
*
* @reasonp - address of the error blocking migration
*
* This function frees *@reasonp and sets it to NULL.
*/
void migrate_del_blocker(Error **reasonp);

/**
* @migrate_add_blocker_normal - prevent normal migration mode from proceeding
*
* @reasonp - address of an error to be returned whenever migration is attempted
*
* @errp - [out] The reason (if any) we cannot block migration right now.
*
* @returns - 0 on success, -EBUSY/-EACCES on failure, with errp set.
*
* *@reasonp is freed and set to NULL if failure is returned.
* On success, the caller must not free @reasonp, except by
* calling migrate_del_blocker.
*/
int migrate_add_blocker_normal(Error **reasonp, Error **errp);

/**
* @migrate_add_blocker_modes - prevent some modes of migration from proceeding
*
* @reasonp - address of an error to be returned whenever migration is attempted
*
* @errp - [out] The reason (if any) we cannot block migration right now.
*
* @mode - one or more migration modes to be blocked. The list is terminated
* by -1 or MIG_MODE_ALL. For the latter, all modes are blocked.
*
* @returns - 0 on success, -EBUSY/-EACCES on failure, with errp set.
*
* *@reasonp is freed and set to NULL if failure is returned.
* On success, the caller must not free *@reasonp before the blocker is removed.
*/
int migrate_add_blocker_modes(Error **reasonp, Error **errp, MigMode mode, ...);

#endif
95 changes: 82 additions & 13 deletions migration/migration.c
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Original file line number Diff line number Diff line change
Expand Up @@ -92,7 +92,7 @@ enum mig_rp_message_type {
static MigrationState *current_migration;
static MigrationIncomingState *current_incoming;

static GSList *migration_blockers;
static GSList *migration_blockers[MIG_MODE__MAX];

static bool migration_object_check(MigrationState *ms, Error **errp);
static int migration_maybe_pause(MigrationState *s,
Expand Down Expand Up @@ -1043,7 +1043,7 @@ static void fill_source_migration_info(MigrationInfo *info)
{
MigrationState *s = migrate_get_current();
int state = qatomic_read(&s->state);
GSList *cur_blocker = migration_blockers;
GSList *cur_blocker = migration_blockers[migrate_mode()];

info->blocked_reasons = NULL;

Expand Down Expand Up @@ -1507,38 +1507,105 @@ int migrate_init(MigrationState *s, Error **errp)
return 0;
}

int migrate_add_blocker_internal(Error **reasonp, Error **errp)
static bool is_busy(Error **reasonp, Error **errp)
{
ERRP_GUARD();

/* Snapshots are similar to migrations, so check RUN_STATE_SAVE_VM too. */
if (runstate_check(RUN_STATE_SAVE_VM) || !migration_is_idle()) {
error_propagate_prepend(errp, *reasonp,
"disallowing migration blocker "
"(migration/snapshot in progress) for: ");
*reasonp = NULL;
return -EBUSY;
return true;
}

migration_blockers = g_slist_prepend(migration_blockers, *reasonp);
return 0;
return false;
}

int migrate_add_blocker(Error **reasonp, Error **errp)
static bool is_only_migratable(Error **reasonp, Error **errp, int modes)
{
if (only_migratable) {
ERRP_GUARD();

if (only_migratable && (modes & BIT(MIG_MODE_NORMAL))) {
error_propagate_prepend(errp, *reasonp,
"disallowing migration blocker "
"(--only-migratable) for: ");
*reasonp = NULL;
return true;
}
return false;
}

static int get_modes(MigMode mode, va_list ap)
{
int modes = 0;

while (mode != -1 && mode != MIG_MODE_ALL) {
assert(mode >= MIG_MODE_NORMAL && mode < MIG_MODE__MAX);
modes |= BIT(mode);
mode = va_arg(ap, MigMode);
}
if (mode == MIG_MODE_ALL) {
modes = BIT(MIG_MODE__MAX) - 1;
}
return modes;
}

static int add_blockers(Error **reasonp, Error **errp, int modes)
{
for (MigMode mode = 0; mode < MIG_MODE__MAX; mode++) {
if (modes & BIT(mode)) {
migration_blockers[mode] = g_slist_prepend(migration_blockers[mode],
*reasonp);
}
}
return 0;
}

int migrate_add_blocker(Error **reasonp, Error **errp)
{
return migrate_add_blocker_modes(reasonp, errp, MIG_MODE_ALL);
}

int migrate_add_blocker_normal(Error **reasonp, Error **errp)
{
return migrate_add_blocker_modes(reasonp, errp, MIG_MODE_NORMAL, -1);
}

int migrate_add_blocker_modes(Error **reasonp, Error **errp, MigMode mode, ...)
{
int modes;
va_list ap;

va_start(ap, mode);
modes = get_modes(mode, ap);
va_end(ap);

if (is_only_migratable(reasonp, errp, modes)) {
return -EACCES;
} else if (is_busy(reasonp, errp)) {
return -EBUSY;
}
return add_blockers(reasonp, errp, modes);
}

return migrate_add_blocker_internal(reasonp, errp);
int migrate_add_blocker_internal(Error **reasonp, Error **errp)
{
int modes = BIT(MIG_MODE__MAX) - 1;

if (is_busy(reasonp, errp)) {
return -EBUSY;
}
return add_blockers(reasonp, errp, modes);
}

void migrate_del_blocker(Error **reasonp)
{
if (*reasonp) {
migration_blockers = g_slist_remove(migration_blockers, *reasonp);
for (MigMode mode = 0; mode < MIG_MODE__MAX; mode++) {
migration_blockers[mode] = g_slist_remove(migration_blockers[mode],
*reasonp);
}
error_free(*reasonp);
*reasonp = NULL;
}
Expand Down Expand Up @@ -1634,12 +1701,14 @@ void qmp_migrate_pause(Error **errp)

bool migration_is_blocked(Error **errp)
{
GSList *blockers = migration_blockers[migrate_mode()];

if (qemu_savevm_state_blocked(errp)) {
return true;
}

if (migration_blockers) {
error_propagate(errp, error_copy(migration_blockers->data));
if (blockers) {
error_propagate(errp, error_copy(blockers->data));
return true;
}

Expand Down
10 changes: 10 additions & 0 deletions stubs/migr-blocker.c
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Original file line number Diff line number Diff line change
Expand Up @@ -6,6 +6,16 @@ int migrate_add_blocker(Error **reasonp, Error **errp)
return 0;
}

int migrate_add_blocker_normal(Error **reasonp, Error **errp)
{
return 0;
}

int migrate_add_blocker_modes(Error **reasonp, Error **errp, MigMode mode, ...)
{
return 0;
}

void migrate_del_blocker(Error **reasonp)
{
}

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