On 12.08.2011 14:31, Matthew Wilcox wrote:
> On Fri, Aug 12, 2011 at 02:14:15PM +0200, Jan Schmidt wrote:
>> (1) Normally, requests to the file system go through ioctls (on the fd
>> of the mountpoint) and the result is small enough to be returned when
>> the ioctl finishes. That said, I thought of passing a user land fd along
>> with this ioctl to the kernel and make it dump the generated bits there.
>> Only, I don't see how to turn a fd into a struct file pointer. And I
>> don't know if that would be considered really ugly by a lot of people.
>
> struct file *filp = fget(fd);
> ...
> fput(filp);
Thanks.
> That said, why not have the ioctl mutate the existing fd?
> ie in userspace:
>
> int fd = open("/mnt/btrfs");
> ioctl(fd, BTRFS_IOC_STREAM);
> while (...) {
> read(fd, buf, 4096);
> ...
> }
> close(fd);
Woo :-) That looks good. I assume from your suggestion at least you do
not consider this too ugly.
One must keep in mind that user space would also be able to open
"/mnt/btrfs/any/file" to achieve the same. An ioctl changing read on a
file (apparently) might me less intuitive. But still, I really like that
approach.
Thanks!
-Jan
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