btrfs: factor out gather_device_info()

Factor out gather_device_info() from __btrfs_alloc_chunk(). This
function iterates over devices list and gather information about
devices. This commit also introduces "max_avail" and
"dev_extent_min" to fold the same calculation to one variable.
This commit has no functional changes.

Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Naohiro Aota <naohiro.aota@wdc.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/volumes.c

@@ -4865,22 +4865,97 @@ static void init_alloc_chunk_ctl(struct btrfs_fs_devices *fs_devices,
 	}
 }
 
+static int gather_device_info(struct btrfs_fs_devices *fs_devices,
+			      struct alloc_chunk_ctl *ctl,
+			      struct btrfs_device_info *devices_info)
+{
+	struct btrfs_fs_info *info = fs_devices->fs_info;
+	struct btrfs_device *device;
+	u64 total_avail;
+	u64 dev_extent_want = ctl->max_stripe_size * ctl->dev_stripes;
+	u64 dev_extent_min = BTRFS_STRIPE_LEN * ctl->dev_stripes;
+	int ret;
+	int ndevs = 0;
+	u64 max_avail;
+	u64 dev_offset;
+
+	/*
+	 * in the first pass through the devices list, we gather information
+	 * about the available holes on each device.
+	 */
+	list_for_each_entry(device, &fs_devices->alloc_list, dev_alloc_list) {
+		if (!test_bit(BTRFS_DEV_STATE_WRITEABLE, &device->dev_state)) {
+			WARN(1, KERN_ERR
+			       "BTRFS: read-only device in alloc_list\n");
+			continue;
+		}
+
+		if (!test_bit(BTRFS_DEV_STATE_IN_FS_METADATA,
+					&device->dev_state) ||
+		    test_bit(BTRFS_DEV_STATE_REPLACE_TGT, &device->dev_state))
+			continue;
+
+		if (device->total_bytes > device->bytes_used)
+			total_avail = device->total_bytes - device->bytes_used;
+		else
+			total_avail = 0;
+
+		/* If there is no space on this device, skip it. */
+		if (total_avail == 0)
+			continue;
+
+		ret = find_free_dev_extent(device, dev_extent_want, &dev_offset,
+					   &max_avail);
+		if (ret && ret != -ENOSPC)
+			return ret;
+
+		if (ret == 0)
+			max_avail = dev_extent_want;
+
+		if (max_avail < dev_extent_min) {
+			if (btrfs_test_opt(info, ENOSPC_DEBUG))
+				btrfs_debug(info,
+			"%s: devid %llu has no free space, have=%llu want=%llu",
+					    __func__, device->devid, max_avail,
+					    dev_extent_min);
+			continue;
+		}
+
+		if (ndevs == fs_devices->rw_devices) {
+			WARN(1, "%s: found more than %llu devices\n",
+			     __func__, fs_devices->rw_devices);
+			break;
+		}
+		devices_info[ndevs].dev_offset = dev_offset;
+		devices_info[ndevs].max_avail = max_avail;
+		devices_info[ndevs].total_avail = total_avail;
+		devices_info[ndevs].dev = device;
+		++ndevs;
+	}
+	ctl->ndevs = ndevs;
+
+	/*
+	 * now sort the devices by hole size / available space
+	 */
+	sort(devices_info, ndevs, sizeof(struct btrfs_device_info),
+	     btrfs_cmp_device_info, NULL);
+
+	return 0;
+}
+
 static int __btrfs_alloc_chunk(struct btrfs_trans_handle *trans,
 			       u64 start, u64 type)
 {
 	struct btrfs_fs_info *info = trans->fs_info;
 	struct btrfs_fs_devices *fs_devices = info->fs_devices;
-	struct btrfs_device *device;
 	struct map_lookup *map = NULL;
 	struct extent_map_tree *em_tree;
 	struct extent_map *em;
 	struct btrfs_device_info *devices_info = NULL;
 	struct alloc_chunk_ctl ctl;
-	u64 total_avail;
+	/* Number of stripes that count for block group size */
-	int data_stripes;	/* number of stripes that count for
+	int data_stripes;
-				   block group size */
 	int ret;
-	int ndevs;
 	int i;
 	int j;
 
@@ -4910,71 +4985,9 @@ static int __btrfs_alloc_chunk(struct btrfs_trans_handle *trans,
 	if (!devices_info)
 		return -ENOMEM;
 
-	/*
+	ret = gather_device_info(fs_devices, &ctl, devices_info);
-	 * in the first pass through the devices list, we gather information
+	if (ret < 0)
-	 * about the available holes on each device.
+		goto error;
-	 */
-	ndevs = 0;
-	list_for_each_entry(device, &fs_devices->alloc_list, dev_alloc_list) {
-		u64 max_avail;
-		u64 dev_offset;
-
-		if (!test_bit(BTRFS_DEV_STATE_WRITEABLE, &device->dev_state)) {
-			WARN(1, KERN_ERR
-			       "BTRFS: read-only device in alloc_list\n");
-			continue;
-		}
-
-		if (!test_bit(BTRFS_DEV_STATE_IN_FS_METADATA,
-					&device->dev_state) ||
-		    test_bit(BTRFS_DEV_STATE_REPLACE_TGT, &device->dev_state))
-			continue;
-
-		if (device->total_bytes > device->bytes_used)
-			total_avail = device->total_bytes - device->bytes_used;
-		else
-			total_avail = 0;
-
-		/* If there is no space on this device, skip it. */
-		if (total_avail == 0)
-			continue;
-
-		ret = find_free_dev_extent(
-			device, ctl.max_stripe_size * ctl.dev_stripes,
-			&dev_offset, &max_avail);
-		if (ret && ret != -ENOSPC)
-			goto error;
-
-		if (ret == 0)
-			max_avail = ctl.max_stripe_size * ctl.dev_stripes;
-
-		if (max_avail < BTRFS_STRIPE_LEN * ctl.dev_stripes) {
-			if (btrfs_test_opt(info, ENOSPC_DEBUG))
-				btrfs_debug(info,
-			"%s: devid %llu has no free space, have=%llu want=%u",
-					    __func__, device->devid, max_avail,
-					    BTRFS_STRIPE_LEN * ctl.dev_stripes);
-			continue;
-		}
-
-		if (ndevs == fs_devices->rw_devices) {
-			WARN(1, "%s: found more than %llu devices\n",
-			     __func__, fs_devices->rw_devices);
-			break;
-		}
-		devices_info[ndevs].dev_offset = dev_offset;
-		devices_info[ndevs].max_avail = max_avail;
-		devices_info[ndevs].total_avail = total_avail;
-		devices_info[ndevs].dev = device;
-		++ndevs;
-	}
-	ctl.ndevs = ndevs;
-
-	/*
-	 * now sort the devices by hole size / available space
-	 */
-	sort(devices_info, ctl.ndevs, sizeof(struct btrfs_device_info),
-	     btrfs_cmp_device_info, NULL);
 
 	/*
 	 * Round down to number of usable stripes, devs_increment can be any