Re: [Tarantool-patches] [PATCH v2 1/5] popen: Introduce a backend engine

[Konstantin Osipov <kostja.osipov@gmail.com>]

> +/**
> + * command_new - allocates a command string from argv array

Would be nice to say why you need to linearise the command at all 
- is it for logging, or error messages, or what?

> + * @argv:	an array with pointers to argv strings
> + * @nr_argv:	number of elements in the @argv
> + *
> + * Returns a new string or NULL on error.
> + */
> +static inline char *
> +command_new(char **argv, size_t nr_argv)

_new/_delete are usually used for classes/objects. command is not
a standalone class, so a better name for the function is
alloc_argv or similar.

having a separate command_free(0) IMO is over-engineering, as well
as separate handle_free and popen_delete(). I would inline
handle_free() and popen_delete() into popen, as well as
handle_new(). If not, I would at least move all free/destroy
functions close together, so that the code is easier to make ends
of - right now popen_delete() as at the end of a long file, while
command_new/handle_new - at the beginnign.

> +ssize_t
> +popen_write(struct popen_handle *handle, void *buf,
> +	    size_t count, unsigned int flags)
> +{
> +	if (!popen_may_io(handle, STDIN_FILENO, flags))
> +		return -1;
> +
> +	if (count > (size_t)SSIZE_MAX) {
> +		errno = E2BIG;
> +		return -1;
> +	}
> +
> +	say_debug("popen: %d: write idx [%s:%d] buf %p count %zu",
> +		  handle->pid, stdX_str(STDIN_FILENO),
> +		  STDIN_FILENO, buf, count);
> +
> +	return write(handle->fds[STDIN_FILENO], buf, count);
> +}

I think popen_write() should work like follows:

 while (not error and not written the full contents of the buffer)
 {
    rc = write()
    // handle errors
    // advance write position
    // if written_size != buf_size coio_fiber_yield_timeout() until the descriptor
    // becomes ready.
 }

For that to work, the descriptor should be set to non-blocking on
parent side right after fork.

Why are you allowing a partial write here? Why are you not
accepting an optional timeout?

> + */
> +static int
> +popen_wait_read(struct popen_handle *handle, int idx, int timeout_msecs)
> +{
> +	struct pollfd pollfd = {
> +		.fd	= handle->fds[idx],
> +		.events	= POLLIN,
> +	};
> +	int ret;
> +
> +	ret = poll(&pollfd, 1, timeout_msecs);

Here you block the event loop for timeout_msecs. Why aren't you
using coio_fiber_yield_timeout()? 

The timeout should be in ev_tstamp format, not integer.

popen_read(), similar to popen_write() should be reading the 
requested amount or error, not return a partial read.

> +#else
> +	/* FIXME: What about FreeBSD/MachO? 

freebsd has fdsecfs
mac has proc_pidinfo()

> 

-- 
Konstantin Osipov, Moscow, Russia