On 11/4/05, Xiangfei Jia <xjianz@xxxxxxxxx> wrote: > > For block devices, the "blkdevs" array is used to hold all the registered > block device drivers, and the maximum number of allowed block drivers is > 255. There is another hash table array called "bdev_hashtable", which is > array of struct "block_device". > > I'm quite confused with these two arrays. (1) what is the relationship > between the "blkdevs" and the "bdev_hashtable"?? blkdevs is an array used internally by block_dev.c (block-device layer) to keep track of registered block devices whereas bdev_hashtable array of type list-head is used to keep information related to block_device in a hash formed which actually hold the struct block_device type pointers/nodes (field bd_hash) > (2) Why a extra sruct, called "block_device" is necessary to be used? > struct block_device is actually there for keeping information about the block_devices like bd_count (how-many times block_device is claimed through bdget function), bd_inode is the inode having data/fields filled with the block_device information see bdget function (http://lxr.linux.no/source/fs/block_dev.c?v=2.4.28#L331), bd_openers is used to keep track of how many times block_device is opened and so other fields too used to keep information related to block_device usage. Just look for struct block_device fields used in block_dev.c file ... I hope my explaination might clear some doubts for you ! By the way these blkdevs and bdev_hashtable (due to their limitations) are removed in 2.6.xx series kernels -- Fawad Lateef -- Kernelnewbies: Help each other learn about the Linux kernel. Archive: http://mail.nl.linux.org/kernelnewbies/ FAQ: http://kernelnewbies.org/faq/
