bio.bi_private是不能儲存私有數據的，內核中會頻繁使用這個成員。
找了好久也就只找到bio.bi_rw：
/*
* bio bi_rw flags
*
* bit 0 -- data direction
* If not set, bio is a read from device. If set, it's a write to device.
* bit 1 -- fail fast device errors
* bit 2 -- fail fast transport errors
* bit 3 -- fail fast driver errors
* bit 4 -- rw-ahead when set
* bit 5 -- barrier
* Insert a serialization point in the IO queue, forcing previously
* submitted IO to be completed before this one is issued.
* bit 6 -- synchronous I/O hint.
* bit 7 -- Unplug the device immediately after submitting this bio.
* bit 8 -- metadata request
* Used for tracing to differentiate metadata and data IO. May also
* get some preferential treatment in the IO scheduler
* bit 9 -- discard sectors
* Informs the lower level device that this range of sectors is no longer
* used by the file system and may thus be freed by the device. Used
* for flash based storage.
* Don't want driver retries for any fast fail whatever the reason.
* bit 10 -- Tell the IO scheduler not to wait for more requests after this
one has been submitted, even if it is a SYNC request.
*/
enum bio_rw_flags {
BIO_RW,
BIO_RW_FAILFAST_DEV,
BIO_RW_FAILFAST_TRANSPORT,
BIO_RW_FAILFAST_DRIVER,
/* above flags must match REQ_* */
BIO_RW_AHEAD,
BIO_RW_BARRIER,
BIO_RW_SYNCIO,
BIO_RW_UNPLUG,
BIO_RW_META,
BIO_RW_DISCARD,
BIO_RW_NOIDLE,
};struct bio {
sector_t bi_sector; /* device address in 512 byte
sectors */
struct bio *bi_next; /* request queue link */
struct block_device *bi_bdev;
unsigned long bi_flags; /* status, command, etc */
unsigned long bi_rw; /* bottom bits READ/WRITE,
* top bits priority
*/
unsigned short bi_vcnt; /* how many bio_vec's */
unsigned short bi_idx; /* current index into bvl_vec */
/* Number of segments in this BIO after
* physical address coalescing is performed.
*/
unsigned int bi_phys_segments;
unsigned int bi_size; /* residual I/O count */
/*
* To keep track of the max segment size, we account for the
* sizes of the first and last mergeable segments in this bio.
*/
unsigned int bi_seg_front_size;
unsigned int bi_seg_back_size;
unsigned int bi_max_vecs; /* max bvl_vecs we can hold */
unsigned int bi_comp_cpu; /* completion CPU */
atomic_t bi_cnt; /* pin count */
struct bio_vec *bi_io_vec; /* the actual vec list */
bio_end_io_t *bi_end_io;
void *bi_private;
#if defined(CONFIG_BLK_DEV_INTEGRITY)
struct bio_integrity_payload *bi_integrity; /* data integrity */
#endif
bio_destructor_t *bi_destructor; /* destructor */
/*
* We can inline a number of vecs at the end of the bio, to avoid
* double allocations for a small number of bio_vecs. This member
* MUST obviously be kept at the very end of the bio.
*/
struct bio_vec bi_inline_vecs[0];
};