On 11/11/12 7:54 PM, Andreas Dilger wrote: > On 2012-11-11, at 3:27 PM, George Spelvin wrote: >> I'm using v1.43-WIP-2012-09-22-10-g41bf599, last commit Oct. 14. >> >> I'm trying to create a file system with 64bit support and specify a >> maximum resize limit of 64 TiB = 2^34 blocks = 17179869184. >> >> (gdb) run -n -t ext4 -O 64bit -E resize=4294967296 /dev/md1 >> Starting program: /root/e2fsprogs/misc/mke2fs -n -t ext4 -O 64bit -E resize=4294967295 /dev/md1 >> [Thread debugging using libthread_db enabled] >> Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1". >> mke2fs 1.43-WIP (22-Sep-2012) >> >> Program received signal SIGFPE, Arithmetic exception. >> 0x0000000000405f5a in parse_extended_opts (opts=<optimized out>, >> param=0x64e200) at mke2fs.c:800 >> 800 gdpb = EXT2_DESC_PER_BLOCK(param); > > This is definitely a bug in the code to do a divide-by-zero. > > However, it should be pointed out that the "resize" option does not > make sense for filesystems larger than 16TB. The mechanism used for > resizing beyond 16TB is different and does not need to reserve blocks. In fairness to the reporter, nothing in the existing ext4 documentation, AFAICT, mentions this. (but then -O 64bit isn't really documented at all) And given that the poor reporter is re-making his whole filesystem just because he found out that he can't grow past 16T: "(wow, was *that* a nasty surprise)" it's understandable that he's trying to give it a rather large resize= value this time around. This is one of those dark corners of weird behavior that could really use some formal docs, at least. :( -Eric > Cheers, Andreas. > >> The issue is that >> >> #define EXT2_DESC_PER_BLOCK(s) (EXT2_BLOCK_SIZE(s) / EXT2_DESC_SIZE(s)) >> #define EXT2_DESC_SIZE(s) \ >> ((EXT2_SB(s)->s_feature_incompat & EXT4_FEATURE_INCOMPAT_64BIT) ? \ >> (s)->s_desc_size : EXT2_MIN_DESC_SIZE) >> >> and s_desc_size is 0 because parse_extended_opts is called from PRS which >> is called very early in main() at line 2320, while s_desc_size is set up >> in ext2fs_initialize, which is not called from main() until mke2fs.c:2353. >> >> As a temporary workaround, I notice that ext2fs_initialize sets s_desc_size to >> the fixed value EXT2_MIN_DESC_SIZE_64BIT, so I changed the #define as follows: >> >> #define EXT2_DESC_SIZE(s) \ >> ((EXT2_SB(s)->s_feature_incompat & EXT4_FEATURE_INCOMPAT_64BIT) ? \ >> (s)->s_desc_size ?: EXT2_MIN_DESC_SIZE_64BIT : EXT2_MIN_DESC_SIZE) >> >> ... which seems to work. >> >> >> (One point that occurred to me while wrestling with this is that the >> default resize limit of initial size * 1000 should perhaps be clamped >> to 2^32 if 64bit is not enabled.) >> -- >> 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 > > > > > > -- > 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
