Hello. Please refer to http://man7.org/linux/man-pages/man2/open.2.html -- the paragraph under EOVERFLOW. It reads that -D_FILE_OFFSET_BITS=64 is required while compiling to access files under size (2<<31)-1 *bits*. This seems to be wrong on two counts: that the numerical value is (2<<30)-1 and not (2<<31)-1, and that the unit should be bytes and not bits. Please see the following transcript from a Kubuntu Trusty 32 bit system on an ext3 filesystem: $ cat test.c # include <stdio.h> int main () { FILE * fp = fopen("toobigfile", "r"); if (fp) printf("Success\n"); else printf("Failure\n"); } $ clang -o test test.c Creating file of size (2<<30)-1 *bytes*: $ truncate -s 2147483647 toobigfile It opens fine: $ strace -f -eopen ./test open("/etc/ld.so.cache", O_RDONLY|O_CLOEXEC) = 3 open("/lib/i386-linux-gnu/libc.so.6", O_RDONLY|O_CLOEXEC) = 3 open("toobigfile", O_RDONLY) = 3 Success +++ exited with 0 +++ Increase it by one byte i.e. to (2<<30) bytes and it fails: $ truncate -s 2147483648 toobigfile $ strace -f -eopen ./test open("/etc/ld.so.cache", O_RDONLY|O_CLOEXEC) = 3 open("/lib/i386-linux-gnu/libc.so.6", O_RDONLY|O_CLOEXEC) = 3 open("toobigfile", O_RDONLY) = -1 EOVERFLOW (Value too large for defined data type) Failure +++ exited with 0 +++ Compile the prog with the prescribed def and it succeeds: $ clang -o test test.c -D_FILE_OFFSET_BITS=64 $ strace -f -eopen ./test open("/etc/ld.so.cache", O_RDONLY|O_CLOEXEC) = 3 open("/lib/i386-linux-gnu/libc.so.6", O_RDONLY|O_CLOEXEC) = 3 open("toobigfile", O_RDONLY|O_LARGEFILE) = 3 Success +++ exited with 0 +++ This shows that the threshold is actually 2 GiB which is (2<<30) *bytes* and not (2<<31) *bits*. Note the difference in both the shift length and units. Note also that (2<<31) bits is (2<<28) bytes which is just 512 MiB and certainly 32-bit apps can access 600 MiB files without special compilation flags. If you find this correct, please update the manpage. If you find this incorrect, please inform me why. Thank you! -- Shriramana Sharma ஶ்ரீரமணஶர்மா श्रीरमणशर्मा -- To unsubscribe from this list: send the line "unsubscribe linux-man" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
