Function zfs_log_write

freebsd/contrib/openzfs/module/zfs/zfs_log.c:534–624

long zfs_immediate_write_sz = 32768;

void
zfs_log_write(zilog_t *zilog, dmu_tx_t *tx, int txtype,
    znode_t *zp, offset_t off, ssize_t resid, int ioflag,
    zil_callback_t callback, void *callback_data)
{
	dmu_buf_impl_t *db = (dmu_buf_impl_t *)sa_get_db(zp->z_sa_hdl);
	uint32_t blocksize = zp->z_blksz;
	itx_wr_state_t write_state;
	uintptr_t fsync_cnt;

	if (zil_replaying(zilog, tx) || zp->z_unlinked ||
	    zfs_xattr_owner_unlinked(zp)) {
		if (callback != NULL)
			callback(callback_data);
		return;
	}

	if (zilog->zl_logbias == ZFS_LOGBIAS_THROUGHPUT)
		write_state = WR_INDIRECT;
	else if (!spa_has_slogs(zilog->zl_spa) &&
	    resid >= zfs_immediate_write_sz)
		write_state = WR_INDIRECT;
	else if (ioflag & (O_SYNC | O_DSYNC))
		write_state = WR_COPIED;
	else
		write_state = WR_NEED_COPY;

	if ((fsync_cnt = (uintptr_t)tsd_get(zfs_fsyncer_key)) != 0) {
		(void) tsd_set(zfs_fsyncer_key, (void *)(fsync_cnt - 1));
	}

	while (resid) {
		itx_t *itx;
		lr_write_t *lr;
		itx_wr_state_t wr_state = write_state;
		ssize_t len = resid;

		/*
		 * A WR_COPIED record must fit entirely in one log block.
		 * Large writes can use WR_NEED_COPY, which the ZIL will
		 * split into multiple records across several log blocks
		 * if necessary.
		 */
		if (wr_state == WR_COPIED &&
		    resid > zil_max_copied_data(zilog))
			wr_state = WR_NEED_COPY;
		else if (wr_state == WR_INDIRECT)
			len = MIN(blocksize - P2PHASE(off, blocksize), resid);

		itx = zil_itx_create(txtype, sizeof (*lr) +
		    (wr_state == WR_COPIED ? len : 0));
		lr = (lr_write_t *)&itx->itx_lr;

		/*
		 * For WR_COPIED records, copy the data into the lr_write_t.
		 */
		if (wr_state == WR_COPIED) {
			int err;