Function arc_release

freebsd/contrib/openzfs/module/zfs/arc.c:6545–6762

* Release this buffer from the cache, making it an anonymous buffer. This * must be done after a read and prior to modifying the buffer contents. * If the buffer has more than one reference, we must make * a new hdr for the buffer. */

 * a new hdr for the buffer.
 */
void
arc_release(arc_buf_t *buf, void *tag)
{
	arc_buf_hdr_t *hdr = buf->b_hdr;

	/*
	 * It would be nice to assert that if its DMU metadata (level >
	 * 0 || it's the dnode file), then it must be syncing context.
	 * But we don't know that information at this level.
	 */

	mutex_enter(&buf->b_evict_lock);

	ASSERT(HDR_HAS_L1HDR(hdr));

	/*
	 * We don't grab the hash lock prior to this check, because if
	 * the buffer's header is in the arc_anon state, it won't be
	 * linked into the hash table.
	 */
	if (hdr->b_l1hdr.b_state == arc_anon) {
		mutex_exit(&buf->b_evict_lock);
		ASSERT(!HDR_IO_IN_PROGRESS(hdr));
		ASSERT(!HDR_IN_HASH_TABLE(hdr));
		ASSERT(!HDR_HAS_L2HDR(hdr));
		ASSERT(HDR_EMPTY(hdr));

		ASSERT3U(hdr->b_l1hdr.b_bufcnt, ==, 1);
		ASSERT3S(zfs_refcount_count(&hdr->b_l1hdr.b_refcnt), ==, 1);
		ASSERT(!list_link_active(&hdr->b_l1hdr.b_arc_node));

		hdr->b_l1hdr.b_arc_access = 0;

		/*
		 * If the buf is being overridden then it may already
		 * have a hdr that is not empty.
		 */
		buf_discard_identity(hdr);
		arc_buf_thaw(buf);

		return;
	}

	kmutex_t *hash_lock = HDR_LOCK(hdr);
	mutex_enter(hash_lock);

	/*
	 * This assignment is only valid as long as the hash_lock is
	 * held, we must be careful not to reference state or the
	 * b_state field after dropping the lock.
	 */
	arc_state_t *state = hdr->b_l1hdr.b_state;
	ASSERT3P(hash_lock, ==, HDR_LOCK(hdr));
	ASSERT3P(state, !=, arc_anon);

	/* this buffer is not on any list */
	ASSERT3S(zfs_refcount_count(&hdr->b_l1hdr.b_refcnt), >, 0);