stat64在64位ubuntu上返回32位st_size

Question

unsigned char *map_file(char *filename, uint64_t *len) {
uint64_t fd = open64(filename, O_RDONLY);

struct stat64 st;
fstat64(fd, &st)

unsigned char *map;
map = (unsigned char *)mmap64(0, st.st_size, PROT_READ, MAP_SHARED, fd, 0);

st.st_size ends up being 4294967295 for large files (I'm testing against 8.7gb file) and is causing segmentation faults (at 47%). Machine is 64-bit and OS (ubuntu) is 64 bit. What am I doing incorrectly?

Answer 1

You probably need to define one of these macros.

http://www.kernel.org/doc/man-pages/online/pages/man7/feature_test_macros.7.html

  _LARGEFILE64_SOURCE
          Expose definitions for the alternative API specified by the LFS (Large
          File Summit) as a "transitional extension" to the Single UNIX
          Specification.  (See http://opengroup.org/platform/lfs.html.)  The
          alternative API consists of a set of new objects (i.e., functions and
          types) whose names are suffixed with "64" (e.g., off64_t versus off_t,
          lseek64() versus lseek(), etc.).  New programs should not employ this
          interface; instead _FILE_OFFSET_BITS=64 should be employed.

  _FILE_OFFSET_BITS
          Defining this macro with the value 64 automatically converts references
          to 32-bit functions and data types related to file I/O and file system
          operations into references to their 64-bit counterparts.  This is
          useful for performing I/O on large files (> 2 Gigabytes) on 32-bit
          systems.  (Defining this macro permits correctly written programs to
          use large files with only a recompilation being required.)  64-bit
          systems naturally permit file sizes greater than 2 Gigabytes, and on
          those systems this macro has no effect.

Answer 2

尝试将-D_FILE_OFFSET_BITS=64添加到编译行。

Answer 3

You should not be using the *64() versions of any of these functions. On 64 bit Linux, off_t is 64 bit, and always has been. Simply use:

    int fd = open(filename, O_RDONLY);
    struct stat st;
    unsigned char *map;

    fstat(fd, &st);
    map = mmap(0, st.st_size, PROT_READ, MAP_SHARED, fd, 0);

(with error-checking, of course). I have tested the above with a > 8GB file, and it works fine.