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struct buffer_head { unsigned long b_state; /* buffer state bitmap (see above)缓冲区状态标志位 */ struct buffer_head *b_this_page;/* circular list of page's buffers页面中的缓冲区 */ struct page *b_page; /* the page this bh is mapped to 存储缓冲区的页面*/ sector_t b_blocknr; /* start block number 其实块号*/ size_t b_size; /* size of mapping 映像的大小*/ char *b_data; /* pointer to data within the page 页面内的数据指针*/ struct block_device *b_bdev; /* 相关联的块设备 */ bh_end_io_t *b_end_io; /* I/O completion I/O完成方法*/ void *b_private; /* reserved for b_end_io io完成方法*/ struct list_head b_assoc_buffers; /* associated with another mapping 相关的映射链表*/ struct address_space *b_assoc_map; /* mapping this buffer is associated with 相关的地址空间*/ atomic_t b_count; /* users using this buffer_head 缓冲区使用计数*/ };
enum bh_state_bits { BH_Uptodate, /* Contains valid data 包含可用数据*/ BH_Dirty, /* Is dirty 脏数据*/ BH_Lock, /* Is locked */ BH_Req, /* Has been submitted for I/O 有IO操作请求*/ BH_Uptodate_Lock,/* Used by the first bh in a page, to serialise * IO completion of other buffers in the page 被IO操作占用 */ BH_Mapped, /* Has a disk mapping 映射了磁盘块*/ BH_New, /* Disk mapping was newly created by get_block 缓冲区用get_block刚刚获取的，还不能使用*/ BH_Async_Read, /* Is under end_buffer_async_read I/O 正在被异步读*/ BH_Async_Write, /* Is under end_buffer_async_write I/O 正在被异步写*/ BH_Delay, /* Buffer is not yet allocated on disk 尚未与磁盘关联*/ BH_Boundary, /* Block is followed by a discontiguity 缓冲区在连续块边缘*/ BH_Write_EIO, /* I/O error on write 写入时遇到错误*/ BH_Unwritten, /* Buffer is allocated on disk but not written */ BH_Quiet, /* Buffer Error Prinks to be quiet 禁止错误*/ BH_Meta, /* Buffer contains metadata */ BH_Prio, /* Buffer should be submitted with REQ_PRIO */ BH_Defer_Completion, /* Defer AIO completion to workqueue */ BH_PrivateStart,/* not a state bit, but the first bit available * for private allocation by other entities */ };
struct buffer_head { unsigned long b_state; /* buffer state bitmap (see above)缓冲区状态标志位 */ struct buffer_head *b_this_page;/* circular list of page's buffers页面中的缓冲区 */ struct page *b_page; /* the page this bh is mapped to 存储缓冲区的页面*/ sector_t b_blocknr; /* start block number 其实块号*/ size_t b_size; /* size of mapping 映像的大小*/ char *b_data; /* pointer to data within the page 页面内的数据指针*/ struct block_device *b_bdev; /* 相关联的块设备 */ bh_end_io_t *b_end_io; /* I/O completion I/O完成方法*/ void *b_private; /* reserved for b_end_io io完成方法*/ struct list_head b_assoc_buffers; /* associated with another mapping 相关的映射链表*/ struct address_space *b_assoc_map; /* mapping this buffer is associated with 相关的地址空间*/ atomic_t b_count; /* users using this buffer_head 缓冲区使用计数*/ }; enum bh_state_bits { BH_Uptodate, /* Contains valid data 包含可用数据*/ BH_Dirty, /* Is dirty 脏数据*/ BH_Lock, /* Is locked */ BH_Req, /* Has been submitted for I/O 有IO操作请求*/ BH_Uptodate_Lock,/* Used by the first bh in a page, to serialise * IO completion of other buffers in the page 被IO操作占用 */ BH_Mapped, /* Has a disk mapping 映射了磁盘块*/ BH_New, /* Disk mapping was newly created by get_block 缓冲区用get_block刚刚获取的，还不能使用*/ BH_Async_Read, /* Is under end_buffer_async_read I/O 正在被异步读*/ BH_Async_Write, /* Is under end_buffer_async_write I/O 正在被异步写*/ BH_Delay, /* Buffer is not yet allocated on disk 尚未与磁盘关联*/ BH_Boundary, /* Block is followed by a discontiguity 缓冲区在连续块边缘*/ BH_Write_EIO, /* I/O error on write 写入时遇到错误*/ BH_Unwritten, /* Buffer is allocated on disk but not written */ BH_Quiet, /* Buffer Error Prinks to be quiet 禁止错误*/ BH_Meta, /* Buffer contains metadata */ BH_Prio, /* Buffer should be submitted with REQ_PRIO */ BH_Defer_Completion, /* Defer AIO completion to workqueue */ BH_PrivateStart,/* not a state bit, but the first bit available * for private allocation by other entities */ }; /* * main unit of I/O for the block layer and lower layers (ie drivers and * stacking drivers) */ struct bio { struct bio *bi_next; /* request queue link 请求链表*/ struct block_device *bi_bdev; /* 相关的块设备 */ unsigned int bi_flags; /* status, command, etc 状态和命令标志 */ int bi_error; unsigned long bi_rw; /* bottom bits READ/WRITE, * top bits priority 读还是写 */ struct bvec_iter bi_iter; /* Number of segments in this BIO after * physical address coalescing is performed. 结合后的片段数目 */ unsigned int bi_phys_segments; /* * To keep track of the max segment size, we account for the * sizes of the first and last mergeable segments in this bio. 第一个可合并的段大小，最后一个可合并的段大小 */ unsigned int bi_seg_front_size; unsigned int bi_seg_back_size; atomic_t __bi_remaining; bio_end_io_t *bi_end_io; /* bi io完成方法 */ void *bi_private; /* 拥有者的私有方法 */ #ifdef CONFIG_BLK_CGROUP /* * Optional ioc and css associated with this bio. Put on bio * release. Read comment on top of bio_associate_current(). */ struct io_context *bi_ioc; struct cgroup_subsys_state *bi_css; #endif union { #if defined(CONFIG_BLK_DEV_INTEGRITY) struct bio_integrity_payload *bi_integrity; /* data integrity */ #endif }; unsigned short bi_vcnt; /* how many bio_vec's bio链表个数*/ /* * Everything starting with bi_max_vecs will be preserved by bio_reset() */ unsigned short bi_max_vecs; /* max bvl_vecs we can hold */ atomic_t __bi_cnt; /* pin count */ struct bio_vec *bi_io_vec; /* the actual vec list bio链表*/ struct bio_set *bi_pool; /* * 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.内嵌bio向量 */ struct bio_vec bi_inline_vecs[0]; };
/* * was unsigned short, but we might as well be ready for > 64kB I/O pages */ struct bio_vec { /* 指向这个缓冲区所驻留的物理页 */ struct page *bv_page; /* 这个缓冲区以字节为单位的大小 */ unsigned int bv_len; /* 缓冲区所驻留的页中以字节为单位的偏移量 */ unsigned int bv_offset; };