Add dmu_tx_hold_append() interface

include/sys/dmu.h

@@ -782,6 +782,9 @@ dmu_tx_t *dmu_tx_create(objset_t *os);
 void dmu_tx_hold_write(dmu_tx_t *tx, uint64_t object, uint64_t off, int len);
 void dmu_tx_hold_write_by_dnode(dmu_tx_t *tx, dnode_t *dn, uint64_t off,
     int len);
+void dmu_tx_hold_append(dmu_tx_t *tx, uint64_t object, uint64_t off, int len);
+void dmu_tx_hold_append_by_dnode(dmu_tx_t *tx, dnode_t *dn, uint64_t off,
+    int len);
 void dmu_tx_hold_clone_by_dnode(dmu_tx_t *tx, dnode_t *dn, uint64_t off,
     int len);
 void dmu_tx_hold_free(dmu_tx_t *tx, uint64_t object, uint64_t off,

include/sys/dmu_tx.h

@@ -91,6 +91,7 @@ enum dmu_tx_hold_type {
 	THT_SPACE,
 	THT_SPILL,
 	THT_CLONE,
+	THT_APPEND,
 	THT_NUMTYPES
 };
 

module/zfs/dmu_tx.c

@@ -294,6 +294,53 @@ dmu_tx_count_write(dmu_tx_hold_t *txh, uint64_t off, uint64_t len)
 	}
 }
 
+static void
+dmu_tx_count_append(dmu_tx_hold_t *txh, uint64_t off, uint64_t len)
+{
+	dnode_t *dn = txh->txh_dnode;
+	int err = 0;
+
+	if (len == 0)
+		return;
+
+	(void) zfs_refcount_add_many(&txh->txh_space_towrite, len, FTAG);
+
+	if (dn == NULL)
+		return;
+
+	/*
+	 * For i/o error checking, read the blocks that will be needed
+	 * to perform the append; first level-0 block (if not aligned, i.e.
+	 * if they are partial-block writes), no additional blocks are read.
+	 */
+	if (dn->dn_maxblkid == 0) {
+		if (off < dn->dn_datablksz &&
+		    (off > 0 || len < dn->dn_datablksz)) {
+			err = dmu_tx_check_ioerr(NULL, dn, 0, 0);
+			if (err != 0) {
+				txh->txh_tx->tx_err = err;
+			}
+		}
+	} else {
+		zio_t *zio = zio_root(dn->dn_objset->os_spa,
+		    NULL, NULL, ZIO_FLAG_CANFAIL);
+
+		/* first level-0 block */
+		uint64_t start = off >> dn->dn_datablkshift;
+		if (P2PHASE(off, dn->dn_datablksz) || len < dn->dn_datablksz) {
+			err = dmu_tx_check_ioerr(zio, dn, 0, start);
+			if (err != 0) {
+				txh->txh_tx->tx_err = err;
+			}
+		}
+
+		err = zio_wait(zio);
+		if (err != 0) {
+			txh->txh_tx->tx_err = err;
+		}
+	}
+}
+
 static void
 dmu_tx_count_dnode(dmu_tx_hold_t *txh)
 {
@@ -334,6 +381,42 @@ dmu_tx_hold_write_by_dnode(dmu_tx_t *tx, dnode_t *dn, uint64_t off, int len)
 	}
 }
 
+/*
+ * Should be used when appending to an object and the exact offset is unknown.
+ * The write must occur at or beyond the specified offset.  Only the L0 block
+ * at provided offset will be prefetched.
+ */
+void
+dmu_tx_hold_append(dmu_tx_t *tx, uint64_t object, uint64_t off, int len)
+{
+	dmu_tx_hold_t *txh;
+
+	ASSERT0(tx->tx_txg);
+	ASSERT3U(len, <=, DMU_MAX_ACCESS);
+
+	txh = dmu_tx_hold_object_impl(tx, tx->tx_objset,
+	    object, THT_APPEND, off, DMU_OBJECT_END);
+	if (txh != NULL) {
+		dmu_tx_count_append(txh, off, len);
+		dmu_tx_count_dnode(txh);
+	}
+}
+
+void
+dmu_tx_hold_append_by_dnode(dmu_tx_t *tx, dnode_t *dn, uint64_t off, int len)
+{
+	dmu_tx_hold_t *txh;
+
+	ASSERT0(tx->tx_txg);
+	ASSERT3U(len, <=, DMU_MAX_ACCESS);
+
+	txh = dmu_tx_hold_dnode_impl(tx, dn, THT_APPEND, off, DMU_OBJECT_END);
+	if (txh != NULL) {
+		dmu_tx_count_append(txh, off, len);
+		dmu_tx_count_dnode(txh);
+	}
+}
+
 /*
  * This function marks the transaction as being a "net free".  The end
  * result is that refquotas will be disabled for this transaction, and
@@ -668,6 +751,26 @@ dmu_tx_dirty_buf(dmu_tx_t *tx, dmu_buf_impl_t *db)
 				if (blkid == 0)
 					match_offset = TRUE;
 				break;
+			case THT_APPEND:
+				if (blkid >= beginblk && (blkid <= endblk ||
+				    txh->txh_arg2 == DMU_OBJECT_END))
+					match_offset = TRUE;
+
+				/*
+				 * THT_WRITE used for bonus and spill blocks.
+				 */
+				ASSERT(blkid != DMU_BONUS_BLKID &&
+				    blkid != DMU_SPILL_BLKID);
+
+				/*
+				 * They might have to increase nlevels,
+				 * thus dirtying the new TLIBs.  Or the
+				 * might have to change the block size,
+				 * thus dirying the new lvl=0 blk=0.
+				 */
+				if (blkid == 0)
+					match_offset = TRUE;
+				break;
 			case THT_FREE:
 				/*
 				 * We will dirty all the level 1 blocks in
@@ -1454,6 +1557,8 @@ dmu_tx_fini(void)
 EXPORT_SYMBOL(dmu_tx_create);
 EXPORT_SYMBOL(dmu_tx_hold_write);
 EXPORT_SYMBOL(dmu_tx_hold_write_by_dnode);
+EXPORT_SYMBOL(dmu_tx_hold_append);
+EXPORT_SYMBOL(dmu_tx_hold_append_by_dnode);
 EXPORT_SYMBOL(dmu_tx_hold_free);
 EXPORT_SYMBOL(dmu_tx_hold_free_by_dnode);
 EXPORT_SYMBOL(dmu_tx_hold_zap);