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ll_rw_block(9) [centos man page]

LL_RW_BLOCK(9)							   The Linux VFS						    LL_RW_BLOCK(9)

ll_rw_block - level access to block devices (DEPRECATED) SYNOPSIS
void ll_rw_block(int rw, int nr, struct buffer_head * bhs[]); ARGUMENTS
rw whether to READ or WRITE or maybe READA (readahead) nr number of struct buffer_heads in the array bhs[] array of pointers to struct buffer_head DESCRIPTION
ll_rw_block takes an array of pointers to struct buffer_heads, and requests an I/O operation on them, either a READ or a WRITE. The third READA option is described in the documentation for generic_make_request which ll_rw_block calls. This function drops any buffer that it cannot get a lock on (with the BH_Lock state bit), any buffer that appears to be clean when doing a write request, and any buffer that appears to be up-to-date when doing read request. Further it marks as clean buffers that are processed for writing (the buffer cache won't assume that they are actually clean until the buffer gets unlocked). ll_rw_block sets b_end_io to simple completion handler that marks the buffer up-to-date (if approriate), unlocks the buffer and wakes any waiters. All of the buffers must be for the same device, and must also be a multiple of the current approved size for the device. COPYRIGHT
Kernel Hackers Manual 3.10 June 2014 LL_RW_BLOCK(9)

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struct_journal_s - this is the concrete type associated with journal_t. SYNOPSIS
struct journal_s { unsigned long j_flags; int j_errno; struct buffer_head * j_sb_buffer; journal_superblock_t * j_superblock; int j_format_version; spinlock_t j_state_lock; int j_barrier_count; transaction_t * j_running_transaction; transaction_t * j_committing_transaction; transaction_t * j_checkpoint_transactions; wait_queue_head_t j_wait_transaction_locked; wait_queue_head_t j_wait_logspace; wait_queue_head_t j_wait_done_commit; wait_queue_head_t j_wait_checkpoint; wait_queue_head_t j_wait_commit; wait_queue_head_t j_wait_updates; struct mutex j_checkpoint_mutex; unsigned int j_head; unsigned int j_tail; unsigned int j_free; unsigned int j_first; unsigned int j_last; struct block_device * j_dev; int j_blocksize; unsigned int j_blk_offset; struct block_device * j_fs_dev; unsigned int j_maxlen; spinlock_t j_list_lock; struct inode * j_inode; tid_t j_tail_sequence; tid_t j_transaction_sequence; tid_t j_commit_sequence; tid_t j_commit_request; tid_t j_commit_waited; __u8 j_uuid[16]; struct task_struct * j_task; int j_max_transaction_buffers; unsigned long j_commit_interval; struct timer_list j_commit_timer; spinlock_t j_revoke_lock; struct jbd_revoke_table_s * j_revoke; struct jbd_revoke_table_s * j_revoke_table[2]; struct buffer_head ** j_wbuf; int j_wbufsize; pid_t j_last_sync_writer; u64 j_average_commit_time; void * j_private; }; MEMBERS
j_flags General journaling state flags j_errno Is there an outstanding uncleared error on the journal (from a prior abort)? j_sb_buffer First part of superblock buffer j_superblock Second part of superblock buffer j_format_version Version of the superblock format j_state_lock Protect the various scalars in the journal j_barrier_count Number of processes waiting to create a barrier lock j_running_transaction The current running transaction.. j_committing_transaction the transaction we are pushing to disk j_checkpoint_transactions a linked circular list of all transactions waiting for checkpointing j_wait_transaction_locked Wait queue for waiting for a locked transaction to start committing, or for a barrier lock to be released j_wait_logspace Wait queue for waiting for checkpointing to complete j_wait_done_commit Wait queue for waiting for commit to complete j_wait_checkpoint Wait queue to trigger checkpointing j_wait_commit Wait queue to trigger commit j_wait_updates Wait queue to wait for updates to complete j_checkpoint_mutex Mutex for locking against concurrent checkpoints j_head Journal head - identifies the first unused block in the journal j_tail Journal tail - identifies the oldest still-used block in the journal. j_free Journal free - how many free blocks are there in the journal? j_first The block number of the first usable block j_last The block number one beyond the last usable block j_dev Device where we store the journal j_blocksize blocksize for the location where we store the journal. j_blk_offset starting block offset for into the device where we store the journal j_fs_dev Device which holds the client fs. For internal journal this will be equal to j_dev j_maxlen Total maximum capacity of the journal region on disk. j_list_lock Protects the buffer lists and internal buffer state. j_inode Optional inode where we store the journal. If present, all journal block numbers are mapped into this inode via bmap. j_tail_sequence Sequence number of the oldest transaction in the log j_transaction_sequence Sequence number of the next transaction to grant j_commit_sequence Sequence number of the most recently committed transaction j_commit_request Sequence number of the most recent transaction wanting commit j_commit_waited Sequence number of the most recent transaction someone is waiting for to commit. j_uuid[16] Uuid of client object. j_task Pointer to the current commit thread for this journal j_max_transaction_buffers Maximum number of metadata buffers to allow in a single compound commit transaction j_commit_interval What is the maximum transaction lifetime before we begin a commit? j_commit_timer The timer used to wakeup the commit thread j_revoke_lock Protect the revoke table j_revoke The revoke table - maintains the list of revoked blocks in the current transaction. j_revoke_table[2] alternate revoke tables for j_revoke j_wbuf array of buffer_heads for journal_commit_transaction j_wbufsize maximum number of buffer_heads allowed in j_wbuf, the number that will fit in j_blocksize j_last_sync_writer most recent pid which did a synchronous write j_average_commit_time the average amount of time in nanoseconds it takes to commit a transaction to the disk. j_private An opaque pointer to fs-private information. AUTHORS
Roger Gammans <rgammans@computer-surgery.co.uk> Author. Stephen Tweedie <sct@redhat.com> Author. COPYRIGHT
Kernel Hackers Manual 3.10 June 2014 STRUCT JOURNAL_S(9)
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