Hi, The xfs_fsr utility in its current state does not support defragmentation of parts of file. Either the entire file is defragmented, or if free space is not available then the operation is not performed. We would like to enhance the utility allowing it to defragment parts of the file, when the free space is not available to defragment the entire file. --------------------------------------------------------------------------------------------------------------- Our initial task was to understand how xfs_fsr currently defragments the file: 1) In /fsr/xfs_fsr.c from main() the control is passed to fsrfile(). In fsrfile(), we open the original file and collect bstat information. A call is then made to fsrfile_common() 2) In fsrfile_common() we check if sufficient free space is available to defragment the file, and if not then we exit. If free space is available, then a call is made to packfile() 3) In packfile(), read_fd_bmap() function provides us with the current number of extents used by the file (cur_nextents) and the ideal number of extents needed to save the file (nextents). In function read_fd_bmap() the the outmap[ ] structure is also populated. 4) packfile() will initially allocate new extents (nextents) to the temporary file and then copy(swap) extents form the existing file. We then fchown() the new temp file and space occupied by the prev fragmented copy is then freed. --------------------------------------------------------------------------------------------------------------- Our understanding to the approach of defragmenting portions of a file is as follows: 1) In fsrfile_common(), a new function will be called when the code determines that there is insufficient free space to defragment the entire file. 2) The new function performs the following tasks: -> Call read_fd_bmap() to get cur_nextents and nextents(ideal). Using nextents we will then have to determine how many extents can be defragmented against the free space available. -> Creating a temp file will not be feasible as it will create a problem when we want to change owners. -> The function will have to hence focus on swapping the existing extents from the fragmented file. For this a swap_extent() function will be needed, which will take arguments as the current extent and the location(in free space) where it needs to be swapped to. For the above functionality Dave suggested that we have a look at EXT4_IOC_MOVE_EXT and its usage. We are however unsure of how to compress the extents which have been chosen for defragmentation and keep the other extents untouched. We are also in doubt about how to proceed without creating a temp file for defragmentation. Any thoughts, comments, opinions etc, are welcome Thank you. Regards A-DRS. _______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs
