* Re: How to lseek the larger file > 2GB under linux
2009-05-17 15:42 ` How to lseek the larger file > 2GB under linux Nicle
@ 2009-05-17 16:20 ` Michal Nazarewicz
[not found] ` <d13fb4990905172137l1a4a9c92k47988da28ad4b7b1@mail.gmail.com>
2009-05-17 18:10 ` LDB
2009-05-17 20:09 ` Glynn Clements
2 siblings, 1 reply; 5+ messages in thread
From: Michal Nazarewicz @ 2009-05-17 16:20 UTC (permalink / raw)
To: Nicle; +Cc: linux-c-programming
[-- Attachment #1: Type: text/plain, Size: 1676 bytes --]
Nicle <ynicle@gmail.com> writes:
> I have a file > 2GB, and my job is seeking the file to pos: 2.1G.
> But, it seems that the lseek64 doesn't work.
> #define _LARGEFILE64_SOURCE
> #include ...
>
> int main() {
> int fd = -1;
> long long pos = (long long) 2*1024*1024*1024 + 10; // over 2G
A long shot, but try (2LL << 30) (the "LL" is important). I don't
expect that will make it work but if you're out of ideas... ;)
> fd = open(FILENAME, O_WRONLY|O_LARGEFILE);
> if (fd < 0) { /* ... */ }
>
> if (lseek64(fd, pos, SEEK_SET) < 0)
> fprintf(stderr, "Failed seeking to %lld, %s\n", pos, strerror(errno));
>
> return 0;
> }
> Then the building cmd: gcc -o test test.c -D_FILE_OFFSET_BITS=64
> Output: > Failed seeking to 2147483658, Success.
>
> The return val of lseek64 was "<0", but the strerror told me "Success".
BTW. The following works fine for me:
#v+
#define _LARGEFILE64_SOURCE
#include <errno.h>
#include <fcntl.h>
#include <stdio.h>
#include <string.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <unistd.h>
#define RUN(expr) if ((expr) < 0) { perror(#expr); return 1; } else (void)0
int main(void) {
const long long pos = (2LL << 30) + 10;
int fd;
RUN(fd = open("deleteme", O_WRONLY | O_LARGEFILE | O_CREAT, 0600));
RUN(lseek64(fd, pos, SEEK_SET));
RUN(write(fd, "a", 1));
return 0;
}
#v-
--
Best regards, _ _
.o. | Liege of Serenly Enlightened Majesty of o' \,=./ `o
..o | Computer Science, Michal "mina86" Nazarewicz (o o)
ooo +--<mina86*tlen.pl>--<jid:mina86*jabber.org>--ooO--(_)--Ooo--
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^ permalink raw reply [flat|nested] 5+ messages in thread* Re: How to lseek the larger file > 2GB under linux
2009-05-17 15:42 ` How to lseek the larger file > 2GB under linux Nicle
2009-05-17 16:20 ` Michal Nazarewicz
@ 2009-05-17 18:10 ` LDB
2009-05-17 20:09 ` Glynn Clements
2 siblings, 0 replies; 5+ messages in thread
From: LDB @ 2009-05-17 18:10 UTC (permalink / raw)
To: Nicle; +Cc: linux-c-programming
Nicle wrote:
> Hi all,
>
> I have a file > 2GB, and my job is seeking the file to pos: 2.1G.
> But, it seems that the lseek64 doesn't work.
> Here is the sample code:
>
> #define _LARGEFILE64_SOURCE
> #include ...
>
> int main()
> {
> int fd = -1;
> long long pos = (long long) 2*1024*1024*1024 + 10; // over 2G
>
> fd = open(FILENAME, O_WRONLY|O_LARGEFILE);
> if (fd < 0){
> ...
> }
>
> if (lseek64(fd, pos, SEEK_SET) < 0) {
> fprintf(stderr, "Failed seeking to %lld, %s\n", pos, strerror(errno));
> }
>
> return 0;
> }
>
> Then the building cmd:
> gcc -o test test.c -D_FILE_OFFSET_BITS=64
>
> Output:
> Failed seeking to 2147483658, Success.
>
> The return val of lseek64 was "<0", but the strerror told me "Success".
> --
> To unsubscribe from this list: send the line "unsubscribe linux-c-programming" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at http://vger.kernel.org/majordomo-info.html
>
>
I changed the below a little, but when I seeked to 2.1GB,
it worked fine. I am not writing like you, but reading.
#define _LARGEFILE64_SOURCE
#include <stdio.h>
#include <sys/types.h>
#include <unistd.h>
#include <stdlib.h>
#include <errno.h>
#include <string.h>
#include <sys/stat.h>
#include <fcntl.h>
int main()
{
int fd, ret;
size_t count = 200;
long long pos = (long long) 2*1024*1024*1024 + 10; // over 2G
char buf[count];
fd = open("/tmp/fish", O_RDONLY|O_LARGEFILE);
if (fd < 0){
fprintf(stderr, "%s\n", strerror(errno));
exit(1);
}
if (lseek64(fd, pos, SEEK_SET) < 0) {
fprintf(stderr, "Failed seeking to %lld, %s\n", pos, strerror(errno));
exit(1);
}
if ((ret = read(fd, buf, count)) < 0) {
fprintf(stderr, "Failed reading: %s\n", strerror(errno));
exit(1);
}
buf[ret] = 0x00;
printf("%s\n", buf);
close(fd);
return 0;
}
^ permalink raw reply [flat|nested] 5+ messages in thread* Re: How to lseek the larger file > 2GB under linux
2009-05-17 15:42 ` How to lseek the larger file > 2GB under linux Nicle
2009-05-17 16:20 ` Michal Nazarewicz
2009-05-17 18:10 ` LDB
@ 2009-05-17 20:09 ` Glynn Clements
2 siblings, 0 replies; 5+ messages in thread
From: Glynn Clements @ 2009-05-17 20:09 UTC (permalink / raw)
To: Nicle; +Cc: linux-c-programming
Nicle wrote:
> I have a file > 2GB, and my job is seeking the file to pos: 2.1G.
> But, it seems that the lseek64 doesn't work.
> Here is the sample code:
[snip]
The following complete program works fine for me:
----------------------------------------------------------------------
#define _LARGEFILE64_SOURCE
#include <stdio.h>
#include <string.h>
#include <errno.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#define FILENAME "test.dat"
int main(void)
{
int fd = -1;
long long pos = (long long) 2*1024*1024*1024 + 10;
fd = open(FILENAME, O_CREAT|O_WRONLY|O_LARGEFILE, 0666);
if (fd < 0) {
perror("open");
return 1;
}
if (lseek64(fd, pos, SEEK_SET) < 0) {
fprintf(stderr, "Failed seeking to %lld, %s\n", pos, strerror(errno));
return 1;
}
return 0;
}
----------------------------------------------------------------------
In general, you should post complete programs which can be compiled
without needing to "fill in the blanks", as the problem may lie in
something which was omitted.
> The return val of lseek64 was "<0", but the strerror told me "Success".
The return value is an off64_t; ensure that it isn't being truncated
to an int, because that will result in a negative value.
In the above, the 0 on the RHS of the comparison should be promoted to
an off64_t automatically (if it isn't, that's a bug in the compiler).
--
Glynn Clements <glynn@gclements.plus.com>
^ permalink raw reply [flat|nested] 5+ messages in thread