int dm_get_device(struct dm_target *ti, const char *path, sector_t start,
sector_t len, int mode, struct dm_dev **result)
{
int r = __table_get_device(ti->table, ti, path,
start, len, mode, result);
if (!r)
dm_set_device_limits(ti, (*result)->bdev);
return r;
}
/**ltl
* 功能: 根据目标设备<major:minor>和起始偏移量获取目标设备对象
* 参数: ti -> 映射目标设备对象
* path -> <major:minor>
* start->映射目标相对低层设备的起始偏移量
* len ->此目标设备在dm设备的长度
* mode ->rw
* result->低层设备对象
* 返回值:
* 说明:
*/
int dm_get_device(struct dm_target *ti, const char *path, sector_t start,
sector_t len, int mode, struct dm_dev **result)
{
/* 初始化映射设备 */
int r = __table_get_device(ti->table, ti, path,
start, len, mode, result);
if (!r) {
request_queue_t *q = bdev_get_queue((*result)->bdev);
struct io_restrictions *rs = &ti->limits;
/*
* Combine the device limits low.
*
* FIXME: if we move an io_restriction struct
* into q this would just be a call to
* combine_restrictions_low()
*/
rs->max_sectors =
min_not_zero(rs->max_sectors, q->max_sectors);
/* FIXME: Device-Mapper on top of RAID-0 breaks because DM
* currently doesn't honor MD's merge_bvec_fn routine.
* In this case, we'll force DM to use PAGE_SIZE or
* smaller I/O, just to be safe. A better fix is in the
* works, but add this for the time being so it will at
* least operate correctly.
*/
if (q->merge_bvec_fn)
rs->max_sectors =
min_not_zero(rs->max_sectors,
(unsigned int) (PAGE_SIZE >> 9));
rs->max_phys_segments =
min_not_zero(rs->max_phys_segments,
q->max_phys_segments);
rs->max_hw_segments =
min_not_zero(rs->max_hw_segments, q->max_hw_segments);
rs->hardsect_size = max(rs->hardsect_size, q->hardsect_size);
rs->max_segment_size =
min_not_zero(rs->max_segment_size, q->max_segment_size);
rs->seg_boundary_mask =
min_not_zero(rs->seg_boundary_mask,
q->seg_boundary_mask);
rs->no_cluster |= !test_bit(QUEUE_FLAG_CLUSTER, &q->queue_flags);
}
