target/file: Add UNMAP emulation support

This patch adds support for emulation of UNMAP within
fd_execute_unmap() backend code.

If the FILEIO backend is normal file, the emulation uses fallocate to
punch hole to reclaim the free space used by the file. If the FILEIO
backend is block device, the emulation uses blkdev_issue_discard().

Cc: Christoph Hellwig <hch@lst.de>
Cc: Martin K. Petersen <martin.petersen@oracle.com>
Cc: Nicholas Bellinger <nab@linux-iscsi.org>
Signed-off-by: Asias He <asias@redhat.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

drivers/target/target_core_file.c

@@ -33,6 +33,7 @@
 #include <linux/falloc.h>
 #include <scsi/scsi.h>
 #include <scsi/scsi_host.h>
+#include <asm/unaligned.h>
 
 #include <target/target_core_base.h>
 #include <target/target_core_backend.h>
@@ -524,6 +525,115 @@ fd_execute_write_same_unmap(struct se_cmd *cmd)
 	return 0;
 }
 
+static sense_reason_t
+fd_execute_unmap(struct se_cmd *cmd)
+{
+	struct se_device *dev = cmd->se_dev;
+	struct fd_dev *fd_dev = FD_DEV(dev);
+	struct file *file = fd_dev->fd_file;
+	struct inode *inode = file->f_mapping->host;
+	unsigned char *buf, *ptr = NULL;
+	sector_t lba;
+	int size;
+	u32 range;
+	sense_reason_t ret = 0;
+	int dl, bd_dl, err;
+
+	/* We never set ANC_SUP */
+	if (cmd->t_task_cdb[1])
+		return TCM_INVALID_CDB_FIELD;
+
+	if (cmd->data_length == 0) {
+		target_complete_cmd(cmd, SAM_STAT_GOOD);
+		return 0;
+	}
+
+	if (cmd->data_length < 8) {
+		pr_warn("UNMAP parameter list length %u too small\n",
+			cmd->data_length);
+		return TCM_PARAMETER_LIST_LENGTH_ERROR;
+	}
+
+	buf = transport_kmap_data_sg(cmd);
+	if (!buf)
+		return TCM_LOGICAL_UNIT_COMMUNICATION_FAILURE;
+
+	dl = get_unaligned_be16(&buf[0]);
+	bd_dl = get_unaligned_be16(&buf[2]);
+
+	size = cmd->data_length - 8;
+	if (bd_dl > size)
+		pr_warn("UNMAP parameter list length %u too small, ignoring bd_dl %u\n",
+			cmd->data_length, bd_dl);
+	else
+		size = bd_dl;
+
+	if (size / 16 > dev->dev_attrib.max_unmap_block_desc_count) {
+		ret = TCM_INVALID_PARAMETER_LIST;
+		goto err;
+	}
+
+	/* First UNMAP block descriptor starts at 8 byte offset */
+	ptr = &buf[8];
+	pr_debug("UNMAP: Sub: %s Using dl: %u bd_dl: %u size: %u"
+		" ptr: %p\n", dev->transport->name, dl, bd_dl, size, ptr);
+
+	while (size >= 16) {
+		lba = get_unaligned_be64(&ptr[0]);
+		range = get_unaligned_be32(&ptr[8]);
+		pr_debug("UNMAP: Using lba: %llu and range: %u\n",
+				 (unsigned long long)lba, range);
+
+		if (range > dev->dev_attrib.max_unmap_lba_count) {
+			ret = TCM_INVALID_PARAMETER_LIST;
+			goto err;
+		}
+
+		if (lba + range > dev->transport->get_blocks(dev) + 1) {
+			ret = TCM_ADDRESS_OUT_OF_RANGE;
+			goto err;
+		}
+
+		if (S_ISBLK(inode->i_mode)) {
+			/* The backend is block device, use discard */
+			struct block_device *bdev = inode->i_bdev;
+
+			err = blkdev_issue_discard(bdev, lba, range, GFP_KERNEL, 0);
+			if (err < 0) {
+				pr_err("FILEIO: blkdev_issue_discard() failed: %d\n",
+						err);
+				ret = TCM_LOGICAL_UNIT_COMMUNICATION_FAILURE;
+				goto err;
+			}
+		} else {
+			/* The backend is normal file, use fallocate */
+			loff_t pos = lba * dev->dev_attrib.block_size;
+			unsigned int len = range * dev->dev_attrib.block_size;
+			int mode = FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE;
+
+			if (!file->f_op->fallocate) {
+				ret = TCM_LOGICAL_UNIT_COMMUNICATION_FAILURE;
+				goto err;
+			}
+			err = file->f_op->fallocate(file, mode, pos, len);
+			if (err < 0) {
+				pr_warn("FILEIO: fallocate() failed: %d\n", err);
+				ret = TCM_LOGICAL_UNIT_COMMUNICATION_FAILURE;
+				goto err;
+			}
+		}
+
+		ptr += 16;
+		size -= 16;
+	}
+
+err:
+	transport_kunmap_data_sg(cmd);
+	if (!ret)
+		target_complete_cmd(cmd, GOOD);
+	return ret;
+}
+
 static sense_reason_t
 fd_execute_rw(struct se_cmd *cmd)
 {
@@ -684,6 +794,7 @@ static struct sbc_ops fd_sbc_ops = {
 	.execute_sync_cache	= fd_execute_sync_cache,
 	.execute_write_same	= fd_execute_write_same,
 	.execute_write_same_unmap = fd_execute_write_same_unmap,
+	.execute_unmap		= fd_execute_unmap,
 };
 
 static sense_reason_t