2011/10/2 Jeff liu <jeff.liu@xxxxxxxxxx>: > > 在 2011-10-2，下午3:59， Andreas Dilger 写道： > >> On 2011-10-01, at 11:41 PM, Jeff liu wrote: >>>> On Sat, Oct 1, 2011 at 10:39 PM, Ted Ts'o <tytso@xxxxxxx> wrote: >>>>> On Sat, Oct 01, 2011 at 10:01:35PM +0800, Dave Young wrote: >>>>>> Hi, >>>>>> >>>>>> Weird problem, when I build app from source, >>>>>> make; make install >>>>>> run the command, but got "cannot execute binary file" >>>>>> >>>>>> hexdump shows the installed binary is full of zero >>>>>> >>>>>> Is it related to ext4 fiemap problem described below? >>>>>> http://lwn.net/Articles/429349/ >>>>> >>>>> There is general agreement that /bin/cp should not have been relying >>>>> on FIEMAP, and I believe the more recent versions of /bin/cp have >>>>> removed that code by default pending implementation of >>>>> SEEK_HOLE/SEEK_DATA. That being said, ext4 had a workaround to its >>>>> FIEMAP implementation that landed in 2.6.39, and you're using >>>>> 3.1.0-rc6. >>> >>> Actually, upstream cp(1) using FIEMAP only if the source file is sparse, or else, it will do normal copy, i.e, block based. >> >> My understanding is that cp uses the blocks count to determine whether the file is sparse or not. > Yes, it based on blocks count to determine that. > >> In the case of delayed allocation (where blocks are not yet allocated, if they are not reflected in the i_blocks count) it might mistakenly think that the file is sparse. I think this might be my case > Thanks for pointing this out, I missed this case. > So for Dave's issue, even if he updated to the upstream Coreutils, this issue will still exists occasionally for delayed allocation, if not run sync in between times. Not occasionally, I can easily reproduce it recently. > >> >> Given the danger of this bug, it is important to ensure ext4 returns DELALLOC extents for pages in the page cache. I think Yongqiang Yang just submitted a patch series to do this for ext4, so it would be important to verify it fixes this problem. > > > Thanks, > -Jeff >> >>>> Do you means It should work in 3.1.0-rc6 even with cp which depends fiemap? >>>> >>>>> >>>>>> I finally managed to find the way to reproduce this: >>>>>> just cp a elf binary A to file B, then cp B to file C, then you will get: >>>>>> A == B != C >>>>>> >>>>>> ie. >>>>>> cp /bin/ls ls1 >>>>>> cp ls1 ls2 >>>>>> >>>>>> ls2 will be filled with zero >>>>> >>>>> If you add a "sync" between the two copies, does that work around the >>>>> problem? I bet it will... >>>> >>>> Yes, it works >>>> >>>>> >>>>> My suggestion is to upgrade to a newer version of coreutils that >>>>> doesn't try to use FIEMAP. >>>> >>>> Thanks, will try >>>> >>>>> >>>>> - Ted >>>>> >>>> >>>> >>>> >>>> -- >>>> Regards >>>> Dave >>>> -- >>>> To unsubscribe from this list: send the line "unsubscribe linux-ext4" in >>>> the body of a message to majordomo@xxxxxxxxxxxxxxx >>>> More majordomo info at http://vger.kernel.org/majordomo-info.html >>> >>> -- >>> To unsubscribe from this list: send the line "unsubscribe linux-ext4" in >>> the body of a message to majordomo@xxxxxxxxxxxxxxx >>> More majordomo info at http://vger.kernel.org/majordomo-info.html >> >> >> Cheers, Andreas >> >> >> >> >> > > -- Regards Dave -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
