read() cant read files larger than 2.1 gig on a 64 bit system

glide creme glidecreme at gmail.com
Fri Dec 25 21:30:46 GMT 2009


Sorry if I'm asking on the wrong mailinglist,
but I've asked on various forums and I havn't found a solution.

I can't read files larger than 2 gig on my ubuntu64bit using posix
'read()', the problem is not related to the allocation itself, which
works.
Attached is a sample program that illustrates this.

I've tried with various, compiler flags like
-D_FILE_OFFSET_BITS=64

According to man 2 read, the maximum is limited by SSIZE_MAX
which is defined in

/usr/include/bits/posix1_lim.h
# define SSIZE_MAX LONG_MAX

And LONG_MAX is defined in /usr/include/limits.h as
# if __WORDSIZE == 64
# define LONG_MAX 9223372036854775807L
# else
# define LONG_MAX 2147483647L
# endif
# define LONG_MIN (-LONG_MAX - 1L)

Thanks

edit:

by the way
$ls -l bigfile.dat
-rw-r--r-- 1 tmp tmp 2163946253 2009-12-23 07:57 bigfile.dat
$ ./a.out
LONG_MAX:9223372036854775807
SSIZE_MAX:9223372036854775807
a.out: Read only 2147479552 of 2163946253 bytes: Succes


readelf -h ./a.out
ELF Header:
  Magic:   7f 45 4c 46 02 01 01 00 00 00 00 00 00 00 00 00
  Class:                             ELF64
  Data:                              2's complement, little endian
  Version:                           1 (current)
  OS/ABI:                            UNIX - System V
  ABI Version:                       0
  Type:                              EXEC (Executable file)
  Machine:                           Advanced Micro Devices X86-64
  Version:                           0x1
  Entry point address:               0x400750
  Start of program headers:          64 (bytes into file)
  Start of section headers:          5312 (bytes into file)
  Flags:                             0x0
  Size of this header:               64 (bytes)
  Size of program headers:           56 (bytes)
  Number of program headers:         9
  Size of section headers:           64 (bytes)
  Number of section headers:         37
  Section header string table index: 34

ldd ./a.out
        linux-vdso.so.1 =>  (0x00007fff689ff000)
        libstdc++.so.6 => /usr/lib/libstdc++.so.6 (0x00007ffee433e000)
        libm.so.6 => /lib/libm.so.6 (0x00007ffee40ba000)
        libgcc_s.so.1 => /lib/libgcc_s.so.1 (0x00007ffee3ea3000)
        libc.so.6 => /lib/libc.so.6 (0x00007ffee3b34000)
        /lib64/ld-linux-x86-64.so.2 (0x00007ffee464e000)

$uname -a
Linux bronco 2.6.31-15-generic #50-Ubuntu SMP Tue Nov 10 14:53:52 UTC
2009 x86_64 GNU/Linux

-------------------------------------------------------------
#include <stdio.h>
#include <stdlib.h>
#include <err.h>
#include <fcntl.h>
#include <sysexits.h>
#include <unistd.h>
#include <sys/stat.h>
#include <limits.h>
#include <bits/posix1_lim.h>
#include <sys/types.h>
// get bytesize of file
size_t fsize(const char* fname){
 struct stat st ;
 stat(fname,&st);
 return st.st_size;
}




int main() {
 const char *infile = "bigfile.dat";
 int fd;
 size_t bytes_read, bytes_expected = fsize(infile);
 char *data;
 printf("LONG_MAX:%lu\n",LONG_MAX);
 printf("SSIZE_MAX:%lu\n",SSIZE_MAX);

 if ((fd = open(infile,O_RDONLY)) < 0)
   err(EX_NOINPUT, "%s", infile);

 if ((data =(char *) malloc(bytes_expected)) == NULL)
   err(EX_OSERR, "data malloc");

 bytes_read = read(fd, data, bytes_expected);

 if (bytes_read != bytes_expected)
   err(EX_DATAERR, "Read only %lu of %lu bytes",bytes_read, bytes_expected);

 /* ... operate on data ... */

 free(data);

 exit(EX_OK);
}



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