block: introduce blk_validate_byte_range()

In preparation to further changes extract a helper function out of
blk_ioctl_discard() that validates if we can do IO against the given
range of disk byte addresses.
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/19a7779323c71e742a2f511e4cf49efcfd68cfd4.1726072086.git.asml.silence@gmail.comSigned-off-by: Jens Axboe <axboe@kernel.dk>

block/ioctl.c

@@ -92,41 +92,54 @@ static int compat_blkpg_ioctl(struct block_device *bdev,
 }
 #endif
 
+/*
+ * Check that [start, start + len) is a valid range from the block device's
+ * perspective, including verifying that it can be correctly translated into
+ * logical block addresses.
+ */
+static int blk_validate_byte_range(struct block_device *bdev,
+				   uint64_t start, uint64_t len)
+{
+	unsigned int bs_mask = bdev_logical_block_size(bdev) - 1;
+	uint64_t end;
+
+	if ((start | len) & bs_mask)
+		return -EINVAL;
+	if (!len)
+		return -EINVAL;
+	if (check_add_overflow(start, len, &end) || end > bdev_nr_bytes(bdev))
+		return -EINVAL;
+
+	return 0;
+}
+
 static int blk_ioctl_discard(struct block_device *bdev, blk_mode_t mode,
 		unsigned long arg)
 {
-	unsigned int bs_mask = bdev_logical_block_size(bdev) - 1;
-	uint64_t range[2], start, len, end;
+	uint64_t range[2], start, len;
 	struct bio *prev = NULL, *bio;
 	sector_t sector, nr_sects;
 	struct blk_plug plug;
 	int err;
 
-	if (!(mode & BLK_OPEN_WRITE))
-		return -EBADF;
-
-	if (!bdev_max_discard_sectors(bdev))
-		return -EOPNOTSUPP;
-	if (bdev_read_only(bdev))
-		return -EPERM;
-
 	if (copy_from_user(range, (void __user *)arg, sizeof(range)))
 		return -EFAULT;
-
 	start = range[0];
 	len = range[1];
 
-	if (!len)
-		return -EINVAL;
-	if ((start | len) & bs_mask)
-		return -EINVAL;
+	if (!bdev_max_discard_sectors(bdev))
+		return -EOPNOTSUPP;
 
-	if (check_add_overflow(start, len, &end) ||
-	    end > bdev_nr_bytes(bdev))
-		return -EINVAL;
+	if (!(mode & BLK_OPEN_WRITE))
+		return -EBADF;
+	if (bdev_read_only(bdev))
+		return -EPERM;
+	err = blk_validate_byte_range(bdev, start, len);
+	if (err)
+		return err;
 
 	filemap_invalidate_lock(bdev->bd_mapping);
-	err = truncate_bdev_range(bdev, mode, start, end - 1);
+	err = truncate_bdev_range(bdev, mode, start, start + len - 1);
 	if (err)
 		goto fail;