Function arc_buf_destroy_impl

freebsd/contrib/openzfs/module/zfs/arc.c:3127–3232

* Free up buf->b_data and pull the arc_buf_t off of the arc_buf_hdr_t's * list and free it. */

 * list and free it.
 */
static void
arc_buf_destroy_impl(arc_buf_t *buf)
{
	arc_buf_hdr_t *hdr = buf->b_hdr;

	/*
	 * Free up the data associated with the buf but only if we're not
	 * sharing this with the hdr. If we are sharing it with the hdr, the
	 * hdr is responsible for doing the free.
	 */
	if (buf->b_data != NULL) {
		/*
		 * We're about to change the hdr's b_flags. We must either
		 * hold the hash_lock or be undiscoverable.
		 */
		ASSERT(HDR_EMPTY_OR_LOCKED(hdr));

		arc_cksum_verify(buf);
		arc_buf_unwatch(buf);

		if (arc_buf_is_shared(buf)) {
			arc_hdr_clear_flags(hdr, ARC_FLAG_SHARED_DATA);
		} else {
			uint64_t size = arc_buf_size(buf);
			arc_free_data_buf(hdr, buf->b_data, size, buf);
			ARCSTAT_INCR(arcstat_overhead_size, -size);
		}
		buf->b_data = NULL;

		ASSERT(hdr->b_l1hdr.b_bufcnt > 0);
		hdr->b_l1hdr.b_bufcnt -= 1;

		if (ARC_BUF_ENCRYPTED(buf)) {
			hdr->b_crypt_hdr.b_ebufcnt -= 1;

			/*
			 * If we have no more encrypted buffers and we've
			 * already gotten a copy of the decrypted data we can
			 * free b_rabd to save some space.
			 */
			if (hdr->b_crypt_hdr.b_ebufcnt == 0 &&
			    HDR_HAS_RABD(hdr) && hdr->b_l1hdr.b_pabd != NULL &&
			    !HDR_IO_IN_PROGRESS(hdr)) {
				arc_hdr_free_abd(hdr, B_TRUE);
			}
		}
	}

	arc_buf_t *lastbuf = arc_buf_remove(hdr, buf);

	if (ARC_BUF_SHARED(buf) && !ARC_BUF_COMPRESSED(buf)) {
		/*
		 * If the current arc_buf_t is sharing its data buffer with the
		 * hdr, then reassign the hdr's b_pabd to share it with the new
		 * buffer at the end of the list. The shared buffer is always
		 * the last one on the hdr's buffer list.
		 *
		 * There is an equivalent case for compressed bufs, but since