Function arc_read

freebsd/contrib/openzfs/module/zfs/arc.c:5906–6451

* "Read" the block at the specified DVA (in bp) via the * cache. If the block is found in the cache, invoke the provided * callback immediately and return. Note that the `zio' parameter * in the callback will be NULL in this case, since no IO was * required. If the block is not in the cache pass the read request * on to the spa with a substitute callback function, so that the * requested

 * for readers of this block.
 */
int
arc_read(zio_t *pio, spa_t *spa, const blkptr_t *bp,
    arc_read_done_func_t *done, void *private, zio_priority_t priority,
    int zio_flags, arc_flags_t *arc_flags, const zbookmark_phys_t *zb)
{
	arc_buf_hdr_t *hdr = NULL;
	kmutex_t *hash_lock = NULL;
	zio_t *rzio;
	uint64_t guid = spa_load_guid(spa);
	boolean_t compressed_read = (zio_flags & ZIO_FLAG_RAW_COMPRESS) != 0;
	boolean_t encrypted_read = BP_IS_ENCRYPTED(bp) &&
	    (zio_flags & ZIO_FLAG_RAW_ENCRYPT) != 0;
	boolean_t noauth_read = BP_IS_AUTHENTICATED(bp) &&
	    (zio_flags & ZIO_FLAG_RAW_ENCRYPT) != 0;
	boolean_t embedded_bp = !!BP_IS_EMBEDDED(bp);
	boolean_t no_buf = *arc_flags & ARC_FLAG_NO_BUF;
	int rc = 0;

	ASSERT(!embedded_bp ||
	    BPE_GET_ETYPE(bp) == BP_EMBEDDED_TYPE_DATA);
	ASSERT(!BP_IS_HOLE(bp));
	ASSERT(!BP_IS_REDACTED(bp));

	/*
	 * Normally SPL_FSTRANS will already be set since kernel threads which
	 * expect to call the DMU interfaces will set it when created.  System
	 * calls are similarly handled by setting/cleaning the bit in the
	 * registered callback (module/os/.../zfs/zpl_*).
	 *
	 * External consumers such as Lustre which call the exported DMU
	 * interfaces may not have set SPL_FSTRANS.  To avoid a deadlock
	 * on the hash_lock always set and clear the bit.
	 */
	fstrans_cookie_t cookie = spl_fstrans_mark();
top:
	if (!embedded_bp) {
		/*
		 * Embedded BP's have no DVA and require no I/O to "read".
		 * Create an anonymous arc buf to back it.
		 */
		hdr = buf_hash_find(guid, bp, &hash_lock);
	}

	/*
	 * Determine if we have an L1 cache hit or a cache miss. For simplicity
	 * we maintain encrypted data separately from compressed / uncompressed
	 * data. If the user is requesting raw encrypted data and we don't have
	 * that in the header we will read from disk to guarantee that we can
	 * get it even if the encryption keys aren't loaded.
	 */
	if (hdr != NULL && HDR_HAS_L1HDR(hdr) && (HDR_HAS_RABD(hdr) ||
	    (hdr->b_l1hdr.b_pabd != NULL && !encrypted_read))) {
		arc_buf_t *buf = NULL;
		*arc_flags |= ARC_FLAG_CACHED;

		if (HDR_IO_IN_PROGRESS(hdr)) {
			zio_t *head_zio = hdr->b_l1hdr.b_acb->acb_zio_head;