Hi there,
I was promised you (viro, hch) have a decided opinion on this topic. The
original mail ("Getting a lot of fs-generated information to user
space") contains a lot of background and is way too long. Point is: I
want to get a bunch of data generated by the kernel (btrfs) to userland
(really).
Matthew Wilcox suggested to use an ioctl changing f_ops.read. Userland
would be like:
> int fd = open("/mnt/btrfs");
> ioctl(fd, BTRFS_IOC_STREAM);
> while (...) {
> read(fd, buf, 4096);
> ...
> }
> close(fd);
To avoid doing buffering myself, I suggested passing a fd to the kernel
where it is expected to dump the generated information, like:
> int fd;
> int pipefd[2];
> struct io_args io_args;
>
> fd = open("/mnt/btrfs");
> pipe(pipefd);
> io_agrs.dest = pipefd[0];
>
> /* thread 1 */
> ioctl(fd, BTRFS_IOC_STREAM, &io_args);
> /* thread 2 */
> while (...) {
> read(pipefd[1], buf, 4096);
> ...
> }
Any opinions on those or different suggestions? Thanks,
-Jan
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