read() wont allow me to read files larger than 2 gig (on a 64bit)

[glide creme]

Thanks for your reply

Yes stat, calculates the filesize correctly,

This is the output of the program

$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

This was I find strange,
because the LONG_MAX is 64bit, and SSIZE_MAX should be defined to be LONG_MAX,
but it looks like read is only limited to 32bit.
-------------------------------------------------------------
#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);
}
-------------------------------------------------------------

On Fri, Dec 25, 2009 at 10:04 AM, AceLan Kao <acelan.kao at canonical.com> wrote:
> Dear Glide,
>
> Does the stat() return the correct file size?
> I remember that there is a 64bits version of stat(), stat64(), maybe
> that's the problem?
>
> Best regards,
> AceLan Kao.
>
> 2009/12/25 glide creme <glidecreme at gmail.com>:
>> Hi
>> 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 '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)
>>
>> Is this the expected behaviour for the read function on a 64bit platform,
>> or is something broken
>>
>> Thanks in advance
>>
>> edit:
>>
>> by the way
>>
>> 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 csi 2.6.31-15-generic #50-Ubuntu SMP Tue Nov 10 14:53:52 UTC
>> 2009 x86_64 GNU/Linux
>>
>> --
>> kernel-team mailing list
>> kernel-team at lists.ubuntu.com
>> https://lists.ubuntu.com/mailman/listinfo/kernel-team
>>
>>
>
>
>
> --
> Chia-Lin Kao(AceLan)
> http://blog.acelan.idv.tw/
> E-Mail: acelan.kaoATcanonical.com (s/AT/@/)
>