On Fri, 2007-08-03 at 10:53 +1000, Mark Harvey wrote: > On 8/3/07, Ming Zhang <blackmagic02881 at gmail.com> wrote: > > On Thu, 2007-08-02 at 14:58 -0400, Pete Wyckoff wrote: > > > markh794 at gmail.com wrote on Tue, 31 Jul 2007 19:57 +1000: > > > > For Variable block SSC device, the block size written needs to be > > > > tracked. > > > [..] > > > > My current thoughts of a solution: > > > > ======================== > > > > A block header describes each block written -> Analogy to the 'tar' > > > > format where a header is written, followed by the 'data' followed by > > > > another header, followed by more data...repeat...until blank header... > > > [..] > > > > However the current implementation for iSCSI -> bs_sync uses a > > > > pread64()/pwrite64() and writes data based on information stored in > > > > scsi_cmd - > > > > pwrite64(fd, cmd->uaddr, cmd->len, cmd->offset) > > > > pread64(fd, cmd->uaddr, cmd->len, cmd->offset) > > > > > > > > > > > > Would it be OK to add a 'blk_header' structure to struct scsi_cmd and if > > > > blk_header is set, write this blk header as well ? > > > > I will attempt to put the above idea into code and submit for comment... > > > > > > I think rather than trying to add stuff to existing backing stores > > > that you should consider writing your own. You need to store both > > > "metadata" (block descriptors) and data, and none of the BSes are > > > set up for that. > > > > > > The complexity of trying to glue in the blk_header so that all BSes > > > know how to tack that on top seems big. Then you have to tell them > > > to read the header, and consider fields in that when determining how > > > much further data to read. It gets messy fast. > > > > also considering tape can have compression and encryption, then each > > block is variable size even in fixed size mode. so support variable size > > is a must eventually. > > Yep. The SSC metadata (header for each tape block) contains a > structure with a 'block type' , size of original data & size of data > stored. > > All accounted for. Just no code for compression or encryption - as yet.. > > enum { > BLK_NOOP, > BLK_UNCOMPRESS_DATA, > BLK_COMPRESSED_DATA, > BLK_ENCRYPTED_DATA, > BLK_FILEMARK, > BLK_BOT, > BLK_EOD, > }; are these bits? can i have multiple bits set like compressed before encryption? also leave room for data deduplication for example storing a token. ;) > struct blk_header { > uint32_t blk_type; > uint32_t blk_size; > uint32_t disk_blk_size; > loff_t blk_number; > loff_t prev_blk; > loff_t curr_blk; > loff_t next_blk; > }; > > > > > In the lu_init for the ssc device, you can change the BS. Then in > > > your READ/WRITE command handler, you can make calls into your own > > > BS that knows how to store this information. (Look out for the > > > allocation size hack in target.c for TYPE_SPT; you may need > > > something similar.) > > > > > > In general, the current separation of backing store from device only > > > really works for block storage. We need an OSD-only backing store > > > for OSD too (not in tree). May be cleaner just to rid the concept > > > of backing store from everything except the device code. > > > > > > -- Pete > > > _______________________________________________ > > > Stgt-devel mailing list > > > Stgt-devel at lists.berlios.de > > > https://lists.berlios.de/mailman/listinfo/stgt-devel > > -- > > Ming Zhang > > > > > > @#$%^ purging memory... (*!% > > http://blackmagic02881.wordpress.com/ > > http://www.linkedin.com/in/blackmagic02881 > > -------------------------------------------- > > > > -- Ming Zhang @#$%^ purging memory... (*!% http://blackmagic02881.wordpress.com/ http://www.linkedin.com/in/blackmagic02881 -------------------------------------------- |