From: Martin Str|mberg <ams AT ludd DOT luth DOT se>
Message-Id: <200110202112.XAA19265@father.ludd.luth.se>
Subject: Re: Resend: DJGPP and files > 2GB
In-Reply-To: <3BC74CBE.EC9CBF9F@phekda.freeserve.co.uk> from Richard Dawe at "Oct 12, 2001 09:04:14 pm"
To: djgpp-workers AT delorie DOT com
Date: Sat, 20 Oct 2001 23:12:36 +0200 (MET DST)
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According to Richard Dawe:
> ---START bigseek.c---
> /*
>  * bigseek.c
>  * Try big relative seeks with DJGPP CVS (aka 2.04?)
>  * Written by Richard Dawe <rich AT phekda DOT freeserve DOT co DOT uk>
>  */
> 
> #include <stdio.h>
> #include <stdlib.h>
> #include <fcntl.h>
> #include <sys/stat.h>
> #include <unistd.h>
> #include <assert.h>
> 
> int
> main (int argc, char *argv[])
> {  
>   char *filename;
>   struct stat sbuf;
>   unsigned long sz;
>   ssize_t n;
>   char buf[4];
>   off_t o;
>   int fd;
> 
>   /* 2GB + 100MB */
>   const unsigned long big_offset = (1024UL * 1024UL * 1024UL * 2UL)
>                                  + (1024UL * 1024UL * 100UL);
> 
>   /* 2GB + 10MB */
>   unsigned long big_offset2 = (1024UL * 1024UL * 1024UL * 2UL)
>                             + (1024UL * 1024UL * 10UL);
> 
>   assert(big_offset2 < big_offset);
> 
>   if (argc < 2) {
>     fprintf(stderr, "Oi! Where's me file?\n");
>     return(EXIT_FAILURE);
>   }
> 
>   /* Does the file exist? How big is it? */
>   filename = argv[1];
> 
>   if (stat(filename, &sbuf) < 0) {
>     perror(argv[0]);
>     return(EXIT_FAILURE);
>   }
> 
>   if (!S_ISREG(sbuf.st_mode)) {
>     fprintf(stderr, "%s is not a regular file!\n", filename);
>     return(EXIT_FAILURE);
>   }
> 
>   /* Check the file's bigger than 2GB. */
>   sz = (unsigned long) sbuf.st_size;
> 
>   if (sz <= big_offset) {
>     fprintf(stderr, "%s is not bigger than %lu (%luMB)!\n",
> 	    filename, big_offset, big_offset / (1024UL * 1024UL));
>     return(EXIT_FAILURE);
>   }
> 
>   /* Now open the file and try out some big relative seeks (> 2GB
> movement). */
>   fd = open(argv[1], O_RDONLY|O_BINARY);
> 
>   o = lseek(fd, big_offset, SEEK_SET);
>   printf("Offset %lu (desired = %lu)\n", (unsigned long) o, big_offset);
>   o = lseek(fd, big_offset2, SEEK_CUR);
>   printf("Offset %lu (desired = %lu)\n", (unsigned long) o,
> 	 big_offset + big_offset2);
> 
>   printf("big_offset - big_offset2 = %lu\n", big_offset - big_offset2);
>   printf("big_offset + big_offset2 = %lu\n", big_offset + big_offset2);
>   printf("(off_t) big_offset2 = %d\n", (off_t) big_offset2);
> 
>   /* Return to the start, seek to beyond 2GB, try a read. Then try
>    * a large (2GB - 1) backwards seek. */
>   o = lseek(fd, 0, SEEK_SET);
>   printf("Offset %d\n", o);
>   o = lseek(fd, big_offset, SEEK_CUR);
>   printf("Offset %d\n", o);
> 
>   n = read(fd, buf, sizeof(buf));
>   if (n < sizeof(buf)) {
>     fprintf(stderr, "Read at offset %d (aka %lu?) failed\n",
> 	    o, (unsigned long) o);
>     close(fd);
>     return(EXIT_FAILURE);
>   } else {
>     printf("Read at offset %d (aka %lu?) OK\n", o, (unsigned long) o);
>   }
>   o = lseek(fd, -sizeof(buf), SEEK_CUR); /* Return to pre-read position */
> 
>   o = lseek(fd, -(off_t)((1024UL * 1024UL * 1024UL * 2UL) - 1UL),
> SEEK_CUR);
>   printf("Offset %d\n", o);
> 
>   printf("big_offset - 2GB - 1 = %lu\n",
> 	 big_offset - ((1024UL * 1024UL * 1024UL * 2UL) - 1UL));
> 
>   /* Done with file */
>   close(fd);
> 
>   return(EXIT_SUCCESS);
> }
> ---END bigseek.c---

Here's the results:

Offset 2252341248 (desired = 2252341248)
Offset 115343360 (desired = 115343360)
big_offset - big_offset2 = 94371840
big_offset + big_offset2 = 115343360
(off_t) big_offset2 = -2136997888
Offset 0
Offset -2042626048
Read at offset -2042626048 (aka 2252341248?) OK
Offset 104857601
big_offset - 2GB - 1 = 104857601


Right,

						MartinS