Hi, >> >> Can anyone please provide me links about the basic explanations of XFS >> basic blocks and filesystem logical block mapping and conversion >> routines? >> >> I tried to understand from code but its not clear to me: >> #define XFS_FSB_TO_BB(mp,fsbno) ((fsbno) << (mp)->m_blkbb_log) > > Convert FileSystem Blocks to Basic Blocks > > FSBs are defined at mkfs time, BBs are always 512 bytes. > >> #define XFS_BB_TO_FSB(mp,bb) \ >> (((bb) + (XFS_FSB_TO_BB(mp,1) - 1)) >> (mp)->m_blkbb_log) > > Convert BB to FSB, rounding up to the next FSB > >> #define XFS_BB_TO_FSBT(mp,bb) ((bb) >> (mp)->m_blkbb_log) > > Convert BB to FSB, rounding down to the FSB containing the BB > >> #define XFS_BB_FSB_OFFSET(mp,bb) ((bb) & ((mp)->m_bsize - 1)) > > Offset of the give BB within a FSB. e.g. if FSB = 4k = 8BB, then > "bb = 5" would return 5, "bb = 63" would return 7... > >> lets consider the last one: >> #define XFS_BB_FSB_OFFSET(mp,bb) ((bb) & ((mp)->m_bsize - 1)) >> >> if basic block (512 byte size) number is 7 and m_bsize is 12 > > m_bsize is the FSB in BB, which will always be a power of 2. > >> (considering FS block size 4096), then this will return 3 [e.g. ( 7 & > > in that case, m_bsize = 8. > >> 11) ]. then what does 3 means here? what offset value it is denoting? > > It's the offset of the BB within the first partial FSB in the range > given. This was once used for sub-block zeroing needed by direct IO, > but is now stale code as the generic DIO layer does this zeroing. > Care to submit a patch to remove that macro? > Thanks Dave. I understand. I am newbie and learning. Sure, i'll create the patch but before let me try out further in the code. Thanks. _______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs
