Re: [PATCH] Replace LFS64 interfaces off64_t and lseek64

[Steven Rostedt <rostedt@goodmis.org>]

On Fri,  6 Jan 2023 17:02:45 -0800
Khem Raj <raj.khem@gmail.com> wrote:

> Musl does not define these interfaces unless -D_LARGEFILE64_SOURCE is
> defined and that too it is transitional until apps switch to using 64bit
> off_t. We pass -D_LARGEFILE64_SOURCE in makefiles already therefore
> original lseek and off_t are already 64bit

I just tested this, and that's not true.

static void pdie(const char *msg)
{
	perror(msg);
	exit(-1);
}

int main (int argc, char **argv)
{
	off_t off;
	int fd;

	argv0 = argv[0];

	if (argc < 2)
		usage();

	printf("off size = %zd\n", sizeof(off));

	fd = open(argv[1], O_RDONLY);
	if (fd < 0)
		pdie("open");
	off = lseek(fd, 0, SEEK_END);
	if (off < 0)
		pdie("lseek");
	printf("offset = %zd\n", off);
	return 0;
}

I compiled the above on a 32bit machine with:

$ gcc -D_LARGEFILE64_SOURCE -o lseek lseek.c
$ ./lseek big-file

Where big-file was 6GBs, and I got this:

off size = 4
lseek: Value too large for defined data type

The _LARGEFILE64_SOURCE just makes the 64 bit versions available. It does
not convert the original ones.

> 
> This fixes build with latest musl which has dropped LFS64 interfaces [1]
> 
> [1] https://git.musl-libc.org/cgit/musl/commit/?id=246f1c811448f37a44b41cd8df8d0ef9736d95f4i
> 
> Signed-off-by: Khem Raj <raj.khem@gmail.com>
> ---

What we could do is add something like:

#ifdef MUSL
# define off64_t off_t
# define lseek64 lseek
[..]
#endif

in one of the headers to make it work with musl.

-- Steve