qemu/block/export/export.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 "block/export.h"
#include "block/nbd.h"
#include "qapi/error.h"
#include "qapi/qapi-commands-block-export.h"

static const BlockExportDriver *blk_exp_drivers[] = {
    &blk_exp_nbd,
};

/* Only accessed from the main thread */
static QLIST_HEAD(, BlockExport) block_exports =
    QLIST_HEAD_INITIALIZER(block_exports);

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)
{
    const BlockExportDriver *drv;
    BlockExport *exp;
    int ret;

    drv = blk_exp_find_driver(export->type);
    if (!drv) {
        error_setg(errp, "No driver found for the requested export type");
        return NULL;
    }

    assert(drv->instance_size >= sizeof(BlockExport));
    exp = g_malloc0(drv->instance_size);
    *exp = (BlockExport) {
        .drv        = drv,
        .refcount   = 1,
    };

    ret = drv->create(exp, export, errp);
    if (ret < 0) {
        g_free(exp);
        return NULL;
    }

    QLIST_INSERT_HEAD(&block_exports, exp, next);
    return exp;
}

/* Callers must hold exp->ctx lock */
void blk_exp_ref(BlockExport *exp)
{
    assert(exp->refcount > 0);
    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);
    g_free(exp);

    aio_context_release(aio_context);
}

/* Callers must hold exp->ctx lock */
void blk_exp_unref(BlockExport *exp)
{
    assert(exp->refcount > 0);
    if (--exp->refcount == 0) {
        /* 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);
    exp->drv->request_shutdown(exp);
    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(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);
}