qemu/block/export/export.c
Stefan Hajnoczi 3d499a43a2 block/export: don't require AioContext lock around blk_exp_ref/unref()
The FUSE export calls blk_exp_ref/unref() without the AioContext lock.
Instead of fixing the FUSE export, adjust blk_exp_ref/unref() so they
work without the AioContext lock. This way it's less error-prone.

Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Message-Id: <20230516190238.8401-15-stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
2023-05-30 17:32:02 +02:00

374 lines
9.2 KiB
C

/*
* Common block export infrastructure
*
* Copyright (c) 2012, 2020 Red Hat, Inc.
*
* Authors:
* Paolo Bonzini <pbonzini@redhat.com>
* Kevin Wolf <kwolf@redhat.com>
*
* This work is licensed under the terms of the GNU GPL, version 2 or
* later. See the COPYING file in the top-level directory.
*/
#include "qemu/osdep.h"
#include "block/block.h"
#include "sysemu/block-backend.h"
#include "sysemu/iothread.h"
#include "block/export.h"
#include "block/fuse.h"
#include "block/nbd.h"
#include "qapi/error.h"
#include "qapi/qapi-commands-block-export.h"
#include "qapi/qapi-events-block-export.h"
#include "qemu/id.h"
#ifdef CONFIG_VHOST_USER_BLK_SERVER
#include "vhost-user-blk-server.h"
#endif
#ifdef CONFIG_VDUSE_BLK_EXPORT
#include "vduse-blk.h"
#endif
static const BlockExportDriver *blk_exp_drivers[] = {
&blk_exp_nbd,
#ifdef CONFIG_VHOST_USER_BLK_SERVER
&blk_exp_vhost_user_blk,
#endif
#ifdef CONFIG_FUSE
&blk_exp_fuse,
#endif
#ifdef CONFIG_VDUSE_BLK_EXPORT
&blk_exp_vduse_blk,
#endif
};
/* Only accessed from the main thread */
static QLIST_HEAD(, BlockExport) block_exports =
QLIST_HEAD_INITIALIZER(block_exports);
BlockExport *blk_exp_find(const char *id)
{
BlockExport *exp;
QLIST_FOREACH(exp, &block_exports, next) {
if (strcmp(id, exp->id) == 0) {
return exp;
}
}
return NULL;
}
static const BlockExportDriver *blk_exp_find_driver(BlockExportType type)
{
int i;
for (i = 0; i < ARRAY_SIZE(blk_exp_drivers); i++) {
if (blk_exp_drivers[i]->type == type) {
return blk_exp_drivers[i];
}
}
return NULL;
}
BlockExport *blk_exp_add(BlockExportOptions *export, Error **errp)
{
bool fixed_iothread = export->has_fixed_iothread && export->fixed_iothread;
const BlockExportDriver *drv;
BlockExport *exp = NULL;
BlockDriverState *bs;
BlockBackend *blk = NULL;
AioContext *ctx;
uint64_t perm;
int ret;
if (!id_wellformed(export->id)) {
error_setg(errp, "Invalid block export id");
return NULL;
}
if (blk_exp_find(export->id)) {
error_setg(errp, "Block export id '%s' is already in use", export->id);
return NULL;
}
drv = blk_exp_find_driver(export->type);
if (!drv) {
error_setg(errp, "No driver found for the requested export type");
return NULL;
}
bs = bdrv_lookup_bs(NULL, export->node_name, errp);
if (!bs) {
return NULL;
}
if (!export->has_writable) {
export->writable = false;
}
if (bdrv_is_read_only(bs) && export->writable) {
error_setg(errp, "Cannot export read-only node as writable");
return NULL;
}
ctx = bdrv_get_aio_context(bs);
aio_context_acquire(ctx);
if (export->iothread) {
IOThread *iothread;
AioContext *new_ctx;
Error **set_context_errp;
iothread = iothread_by_id(export->iothread);
if (!iothread) {
error_setg(errp, "iothread \"%s\" not found", export->iothread);
goto fail;
}
new_ctx = iothread_get_aio_context(iothread);
/* Ignore errors with fixed-iothread=false */
set_context_errp = fixed_iothread ? errp : NULL;
ret = bdrv_try_change_aio_context(bs, new_ctx, NULL, set_context_errp);
if (ret == 0) {
aio_context_release(ctx);
aio_context_acquire(new_ctx);
ctx = new_ctx;
} else if (fixed_iothread) {
goto fail;
}
}
/*
* Block exports are used for non-shared storage migration. Make sure
* that BDRV_O_INACTIVE is cleared and the image is ready for write
* access since the export could be available before migration handover.
* ctx was acquired in the caller.
*/
bdrv_activate(bs, NULL);
perm = BLK_PERM_CONSISTENT_READ;
if (export->writable) {
perm |= BLK_PERM_WRITE;
}
blk = blk_new(ctx, perm, BLK_PERM_ALL);
if (!fixed_iothread) {
blk_set_allow_aio_context_change(blk, true);
}
ret = blk_insert_bs(blk, bs, errp);
if (ret < 0) {
goto fail;
}
if (!export->has_writethrough) {
export->writethrough = false;
}
blk_set_enable_write_cache(blk, !export->writethrough);
assert(drv->instance_size >= sizeof(BlockExport));
exp = g_malloc0(drv->instance_size);
*exp = (BlockExport) {
.drv = drv,
.refcount = 1,
.user_owned = true,
.id = g_strdup(export->id),
.ctx = ctx,
.blk = blk,
};
ret = drv->create(exp, export, errp);
if (ret < 0) {
goto fail;
}
assert(exp->blk != NULL);
QLIST_INSERT_HEAD(&block_exports, exp, next);
aio_context_release(ctx);
return exp;
fail:
if (blk) {
blk_set_dev_ops(blk, NULL, NULL);
blk_unref(blk);
}
aio_context_release(ctx);
if (exp) {
g_free(exp->id);
g_free(exp);
}
return NULL;
}
void blk_exp_ref(BlockExport *exp)
{
assert(qatomic_read(&exp->refcount) > 0);
qatomic_inc(&exp->refcount);
}
/* Runs in the main thread */
static void blk_exp_delete_bh(void *opaque)
{
BlockExport *exp = opaque;
AioContext *aio_context = exp->ctx;
aio_context_acquire(aio_context);
assert(exp->refcount == 0);
QLIST_REMOVE(exp, next);
exp->drv->delete(exp);
blk_set_dev_ops(exp->blk, NULL, NULL);
blk_unref(exp->blk);
qapi_event_send_block_export_deleted(exp->id);
g_free(exp->id);
g_free(exp);
aio_context_release(aio_context);
}
void blk_exp_unref(BlockExport *exp)
{
assert(qatomic_read(&exp->refcount) > 0);
if (qatomic_fetch_dec(&exp->refcount) == 1) {
/* Touch the block_exports list only in the main thread */
aio_bh_schedule_oneshot(qemu_get_aio_context(), blk_exp_delete_bh,
exp);
}
}
/*
* Drops the user reference to the export and requests that all client
* connections and other internally held references start to shut down. When
* the function returns, there may still be active references while the export
* is in the process of shutting down.
*
* Acquires exp->ctx internally. Callers must *not* hold the lock.
*/
void blk_exp_request_shutdown(BlockExport *exp)
{
AioContext *aio_context = exp->ctx;
aio_context_acquire(aio_context);
/*
* If the user doesn't own the export any more, it is already shutting
* down. We must not call .request_shutdown and decrease the refcount a
* second time.
*/
if (!exp->user_owned) {
goto out;
}
exp->drv->request_shutdown(exp);
assert(exp->user_owned);
exp->user_owned = false;
blk_exp_unref(exp);
out:
aio_context_release(aio_context);
}
/*
* Returns whether a block export of the given type exists.
* type == BLOCK_EXPORT_TYPE__MAX checks for an export of any type.
*/
static bool blk_exp_has_type(BlockExportType type)
{
BlockExport *exp;
if (type == BLOCK_EXPORT_TYPE__MAX) {
return !QLIST_EMPTY(&block_exports);
}
QLIST_FOREACH(exp, &block_exports, next) {
if (exp->drv->type == type) {
return true;
}
}
return false;
}
/* type == BLOCK_EXPORT_TYPE__MAX for all types */
void blk_exp_close_all_type(BlockExportType type)
{
BlockExport *exp, *next;
assert(in_aio_context_home_thread(qemu_get_aio_context()));
QLIST_FOREACH_SAFE(exp, &block_exports, next, next) {
if (type != BLOCK_EXPORT_TYPE__MAX && exp->drv->type != type) {
continue;
}
blk_exp_request_shutdown(exp);
}
AIO_WAIT_WHILE_UNLOCKED(NULL, blk_exp_has_type(type));
}
void blk_exp_close_all(void)
{
blk_exp_close_all_type(BLOCK_EXPORT_TYPE__MAX);
}
void qmp_block_export_add(BlockExportOptions *export, Error **errp)
{
blk_exp_add(export, errp);
}
void qmp_block_export_del(const char *id,
bool has_mode, BlockExportRemoveMode mode,
Error **errp)
{
ERRP_GUARD();
BlockExport *exp;
exp = blk_exp_find(id);
if (exp == NULL) {
error_setg(errp, "Export '%s' is not found", id);
return;
}
if (!exp->user_owned) {
error_setg(errp, "Export '%s' is already shutting down", id);
return;
}
if (!has_mode) {
mode = BLOCK_EXPORT_REMOVE_MODE_SAFE;
}
if (mode == BLOCK_EXPORT_REMOVE_MODE_SAFE &&
qatomic_read(&exp->refcount) > 1) {
error_setg(errp, "export '%s' still in use", exp->id);
error_append_hint(errp, "Use mode='hard' to force client "
"disconnect\n");
return;
}
blk_exp_request_shutdown(exp);
}
BlockExportInfoList *qmp_query_block_exports(Error **errp)
{
BlockExportInfoList *head = NULL, **tail = &head;
BlockExport *exp;
QLIST_FOREACH(exp, &block_exports, next) {
BlockExportInfo *info = g_new(BlockExportInfo, 1);
*info = (BlockExportInfo) {
.id = g_strdup(exp->id),
.type = exp->drv->type,
.node_name = g_strdup(bdrv_get_node_name(blk_bs(exp->blk))),
.shutting_down = !exp->user_owned,
};
QAPI_LIST_APPEND(tail, info);
}
return head;
}