determining size of cdrom

[Jeff Meininger]

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I'm trying to determine the raw size of a cdrom disc, as in the size of
the file you'd get by doing 'dd if=/dev/cdrom of=size_of_this.img'.

I've tried the following things (with a disc in the drive) without
success, and I'm hoping that someone will be able to point me in the right
direction.

struct stat s;
stat("/dev/cdrom", &s);
/* s.st_size is 0, s.st_blocks is 0.  */

int fd = open("/dev/cdrom", O_RDONLY);

off_t bytes = lseek(fd, 0, SEEK_END);
/* bytes is 0 */

long sectors = 0;
ioctl(fd, BLKGETSIZE, &sectors);
/* sectors varies (never seems accurate) and is usually LONG_MAX */
	
long ssz = 0;
ioctl(fd, BLKSSZGET, &ssz);
/* ssz varies, and is usually 1024. (shouldn't it be 2048?)  */

/* ioctl HDIO_GETGEO fails. */

/* ioctl HDIO_GET_IDENTITY returns 0's for the c/h/s values I'm looking
for.  */

I didn't find anything that looked obvious to me in linux/cdrom.h, except
in the #ifdef __KERNEL__ section which I don't believe I can use from
user space.

I hope I didn't miss something really obvious, but I've been at this
problem for a few days now (mostly spent reading docs and headers) and I'm
at the point where I'll risk asking something stupid.

Thanks!!

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copy of your replies straight to my email address: [e-mail].