-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 On 02/16/2012 05:58 PM, Ted Ts'o wrote: > I don't see the bug here. If there are no leftover sparse bytes, > there's no need to write the last zero byte. The whole point was to > make sure i_size was set correctly, and if sparse==0, then i_size is > correct. - From what I can see, when sparse == 0, the last write does a seek to move the file pointer, but doesn't write anything beyond the last hole, so i_size is not updated. This resulted in an image file I took of a 20gb fs being 124 MiB too small. I can only assume that this is to be expected, and is the reason for passing one byte of zero_buff to write_block instead of not giving it any bytes to write, and just asking it to do the seek the way the loop does. > ftruncate() happens to work today for Linux, but it's not guaranteed > to do anything on all operating systems or even all file systems. Per > the standards spec: > > If the file previously was smaller than this size, ftruncate() > shall either increase the size of the file or fail. > > Speaking of which, you're not checking the return value from ftruncate > in your patch. So I'd be happy if you checked ftruncate, and if it > failed, falling back to the > > if (sparse) > write_block(fd, zero_buf, sparse-1, 1, -1); > > code path. That way, if ftruncate() happens to fail on NFS, or ceph, > or some random file system that chose to meet the standards spec, but > by failing if someone tries to increase the size of the file using > ftruncate. (Or some other OS; there are other operating systems, > including GNU Hurd and BSD, and I don't know for sure how ftruncate > behaves on all of those other OS's and file systems.) Good idea. -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.11 (GNU/Linux) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org/ iQEcBAEBAgAGBQJPPY0BAAoJEJrBOlT6nu75ZpQH+QH0OGFfY0Tde0SZ3gl1QPeo pbzYRA6Io6uxOMqLwYlOxfmxoaHByuQQupVDAyNtSLVEdGXvaixTNH/omu4TTYcR 54YARfgnsNlpfiJ8cYEP5jqNUvvIfqjqgBZncFYGiP/1smMh8uz56ThkHJtjaaSV hEs1R9F6PdF+cplmsQooRAWedIR8f/Nd9KncKaKHOPiUKDr+3kbneBfbYMrqz6U9 ftoKVYNXNIb0+u9KxOFZybYMkiKoDQrMIUDkXCI39Mgkga/+3SelDZ+vl9Ax142e oEAQfC6RrI86Oh+OjF3YeBQdreyz4ddkEnjFv/EgsfW8PPBw+iYt1NiaXiCUgd4= =Kz4m -----END PGP SIGNATURE----- -- 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
