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Block Device

Outline. Block device operationsGeneric block device layerSkeleton of a block device driverReference. What will we learn ?. From this report, we learnThe details of how a block device worksll_rw_block() : trigger I/O transfer __make_request (): make request -> request queue task queue : plug/

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Block Device

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    1. Block Device Q36921204 ??? Q36921115 ???

    2. Outline Block device operations Generic block device layer Skeleton of a block device driver Reference

    3. What will we learn ? From this report, we learn The details of how a block device works ll_rw_block() : trigger I/O transfer __make_request (): make request -> request queue task queue : plug/unplug use the mechanism request service routine : How to write a block device driver writing a module Init / exit implement the necessary operations block_device_operations request_fn_proc

    4. Common Block Device Operations In fs/block_dev.c struct file_operations def_blk_fops = { open: blkdev_open, release: blkdev_close, llseek: block_llseek, read: generic_file_read, write: generic_file_write, mmap: generic_file_mmap, fsync: block_fsync, ioctl: blkdev_ioctl, };

    5. Block Device Specific Operations Additional operations for block device only In include/linux/fs.h : struct block_device_operations { int (*open) (struct inode *, struct file *); int (*release) (struct inode *, struct file *); int (*ioctl) (struct inode *, struct file *, unsigned, unsigned long); int (*check_media_change) (kdev_t); int (*revalidate) (kdev_t); struct module *owner; }; In include/linux/blkdev.h : typedef void (request_fn_proc) (request_queue_t *q);

    9. Generic Block Device Layer Provides common functionality for all block devices in Linux Uniform interface (to file system) e.g. bread( ) block_prepare_write( ) block_read_full_page( ) ll_rw_block( ) buffer management and disk caching Block I/O requests scheduling Generates and queues actual I/O requests in a request queue (per device) Individual device driver services this queue (likely interrupt driven)

    10. Request Queue Data structure: in include/linux/blkdev.h Queue header: type request_queue_t typedef structure request_queue request_queue_t queue_head: double linked list of pending requests request_fn: pointer to request service routine Queue element: struct request cmd: read or write Number of request sectors, segments bh, bhtail: a list of buffer header Memory area (for I/O transfer)

    11. Request Queue

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