Function vdev_cache_read

freebsd/contrib/openzfs/module/zfs/vdev_cache.c:250–324

* Read data from the cache. Returns B_TRUE cache hit, B_FALSE on miss. */

 * Read data from the cache.  Returns B_TRUE cache hit, B_FALSE on miss.
 */
boolean_t
vdev_cache_read(zio_t *zio)
{
	vdev_cache_t *vc = &zio->io_vd->vdev_cache;
	vdev_cache_entry_t *ve, *ve_search;
	uint64_t cache_offset = P2ALIGN(zio->io_offset, VCBS);
	zio_t *fio;
	uint64_t cache_phase __maybe_unused = P2PHASE(zio->io_offset, VCBS);

	ASSERT3U(zio->io_type, ==, ZIO_TYPE_READ);

	if (zio->io_flags & ZIO_FLAG_DONT_CACHE)
		return (B_FALSE);

	if (zio->io_size > zfs_vdev_cache_max)
		return (B_FALSE);

	/*
	 * If the I/O straddles two or more cache blocks, don't cache it.
	 */
	if (P2BOUNDARY(zio->io_offset, zio->io_size, VCBS))
		return (B_FALSE);

	ASSERT3U(cache_phase + zio->io_size, <=, VCBS);

	mutex_enter(&vc->vc_lock);

	ve_search = kmem_alloc(sizeof (vdev_cache_entry_t), KM_SLEEP);
	ve_search->ve_offset = cache_offset;
	ve = avl_find(&vc->vc_offset_tree, ve_search, NULL);
	kmem_free(ve_search, sizeof (vdev_cache_entry_t));

	if (ve != NULL) {
		if (ve->ve_missed_update) {
			mutex_exit(&vc->vc_lock);
			return (B_FALSE);
		}

		if ((fio = ve->ve_fill_io) != NULL) {
			zio_vdev_io_bypass(zio);
			zio_add_child(zio, fio);
			mutex_exit(&vc->vc_lock);
			VDCSTAT_BUMP(vdc_stat_delegations);
			return (B_TRUE);
		}

		vdev_cache_hit(vc, ve, zio);
		zio_vdev_io_bypass(zio);

		mutex_exit(&vc->vc_lock);
		VDCSTAT_BUMP(vdc_stat_hits);
		return (B_TRUE);
	}

	ve = vdev_cache_allocate(zio);

	if (ve == NULL) {
		mutex_exit(&vc->vc_lock);