On 11/29/2012 02:53 PM, Jim Meyering wrote: > Jeff Liu wrote: > >> On 11/29/2012 12:15 PM, Jim Meyering wrote: >>> Hugh Dickins wrote: >>>> On Thu, 29 Nov 2012, Jaegeuk Hanse wrote: >>> ... >>>>> But this time in which scenario will use it? >>>> >>>> I was not very convinced by the grep argument from Jim and Paul: >>>> that seemed to be grep holding on to a no-arbitrary-limits dogma, >>>> at the expense of its users, causing an absurd line-length issue, >>>> which use of SEEK_DATA happens to avoid in some cases. >>>> >>>> The cp of sparse files from Jeff and Dave was more convincing; >>>> but I still didn't see why little old tmpfs needed to be ahead >>>> of the pack. >>>> >>>> But at LinuxCon/Plumbers in San Diego in August, a more convincing >>>> case was made: I was hoping you would not ask, because I did not take >>>> notes, and cannot pass on the details - was it rpm building on tmpfs? >>>> I was convinced enough to promise support on tmpfs when support on >>>> ext4 goes in. >>> >>> Re the cp-vs-sparse-file case, the current FIEMAP-based code in GNU >>> cp is ugly and complicated enough that until recently it harbored a >>> hard-to-reproduce data-corrupting bug[*]. Now that SEEK_DATA/SEEK_HOLE >>> support work will work also for tmpfs and ext4, we can plan to remove >>> the FIEMAP-based code in favor of a simpler SEEK_DATA/SEEK_HOLE-based >>> implementation. >> How do we teach du(1) to aware of the real disk footprint with Btrfs >> clone or OCFS2 reflinked files if we remove the FIEMAP-based code? >> >> How about if we still keep it there, and introduce SEEK_DATA/SEEK_HOLE >> code to the extent-scan module which is dedicated to deal with sparse files? > > Hi Jeff, > By "removing the FIEMAP-based code" I mean the uses in copy.c. > All of that should remain independent of how du does its job, > so if FIEMAP is required for your planned du enhancement, > then feel free to use it. Hi Jim, Thanks for the clarification, that's fine. :) Regards, -Jeff > -- > To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>