Re: [Tarantool-patches] [PATCH 12/12] popen: allow to close parent's end of std* fds

[Cyrill Gorcunov <gorcunov@gmail.com>]

On Tue, Apr 14, 2020 at 02:38:21PM +0300, Alexander Turenko wrote:
> The function popen_shutdown() checks whether std{in,out,err} was piped
> and closes the parent's end. A user should have ability to send EOF for
> child's stdin for stream programs like `grep`. It is better when there
> is a function that encapsulates proper checks, error messages and the
> actual actions.
> 
> This commit in particular reverts
> 1ef95b99f6553b246729e7bb5bdc19038043db74 ('popen: remove redundant fd
> check before perform IO'), because now the check is meaningful: an fd
> may become closed before the whole popen handle will be deleted.
> 
> Part of #4031
> ---
>  src/lib/core/popen.c | 170 ++++++++++++++++++++++++++++++++-----------
>  src/lib/core/popen.h |   3 +
>  2 files changed, 130 insertions(+), 43 deletions(-)
> 
> diff --git a/src/lib/core/popen.c b/src/lib/core/popen.c
> index 640dffc2b..8760429c2 100644
> --- a/src/lib/core/popen.c
> +++ b/src/lib/core/popen.c
> @@ -34,6 +34,43 @@ static RLIST_HEAD(popen_head);
>  static int dev_null_fd_ro = -1;
>  static int dev_null_fd_wr = -1;
>  
> +static const struct {
> +	unsigned int	mask;
> +	unsigned int	mask_devnull;
> +	unsigned int	mask_close;
> +	int		fileno;
> +	int		*dev_null_fd;
> +	int		parent_idx;
> +	int		child_idx;
> +	bool		nonblock;
> +} pfd_map[POPEN_FLAG_FD_STDEND_BIT] = {
> +	{
> +		.mask		= POPEN_FLAG_FD_STDIN,
> +		.mask_devnull	= POPEN_FLAG_FD_STDIN_DEVNULL,
> +		.mask_close	= POPEN_FLAG_FD_STDIN_CLOSE,
> +		.fileno		= STDIN_FILENO,
> +		.dev_null_fd	= &dev_null_fd_ro,
> +		.parent_idx	= 1,
> +		.child_idx	= 0,
> +	}, {
> +		.mask		= POPEN_FLAG_FD_STDOUT,
> +		.mask_devnull	= POPEN_FLAG_FD_STDOUT_DEVNULL,
> +		.mask_close	= POPEN_FLAG_FD_STDOUT_CLOSE,
> +		.fileno		= STDOUT_FILENO,
> +		.dev_null_fd	= &dev_null_fd_wr,
> +		.parent_idx	= 0,
> +		.child_idx	= 1,
> +	}, {
> +		.mask		= POPEN_FLAG_FD_STDERR,
> +		.mask_devnull	= POPEN_FLAG_FD_STDERR_DEVNULL,
> +		.mask_close	= POPEN_FLAG_FD_STDERR_CLOSE,
> +		.fileno		= STDERR_FILENO,
> +		.dev_null_fd	= &dev_null_fd_wr,
> +		.parent_idx	= 0,
> +		.child_idx	= 1,
> +	},
> +};
> +
>  /**
>   * Register popen handle in a pids map.
>   */
> @@ -213,7 +250,8 @@ handle_free(struct popen_handle *handle)
>   * Returns 0 if so and -1 otherwise (and set a diag).
>   */
>  static inline int
> -popen_may_io(struct popen_handle *handle, unsigned int io_flags)
> +popen_may_io(struct popen_handle *handle, unsigned int idx,
> +	     unsigned int io_flags, bool allow_closed)
>  {
>  	if (!(io_flags & handle->flags)) {
>  		diag_set(IllegalParams, "popen: handle does not support the "
> @@ -221,6 +259,12 @@ popen_may_io(struct popen_handle *handle, unsigned int io_flags)
>  		return -1;
>  	}
>  
> +       if (! allow_closed && handle->ios[idx].fd < 0) {
> +	       diag_set(IllegalParams, "popen: attempt to operate on a closed "
> +			"file descriptor");
> +               return -1;
> +       }
> +
>  	return 0;
>  }
>  
> @@ -299,6 +343,7 @@ stdX_str(unsigned int index)
>   *   - count: data is too big.
>   *   - flags: POPEN_FLAG_FD_STDIN bit is unset.
>   *   - handle: handle does not support the requested IO operation.
> + *   - handle: attempt to operate on a closed fd.
>   * - SocketError: an IO error occurs at write().
>   * - TimedOut: @a timeout quota is exceeded.
>   * - FiberIsCancelled: cancelled by an outside code.
> @@ -327,11 +372,11 @@ popen_write_timeout(struct popen_handle *handle, const void *buf,
>  		return -1;
>  	}
>  
> -	if (popen_may_io(handle, flags) != 0)
> -		return -1;
> -
>  	int idx = STDIN_FILENO;
>  
> +	if (popen_may_io(handle, idx, flags, false) != 0)
> +		return -1;
> +
>  	say_debug("popen: %d: write idx [%s:%d] buf %p count %zu "
>  		  "fds %d timeout %.9g",
>  		  handle->pid, stdX_str(idx), idx, buf, count,
> @@ -362,6 +407,7 @@ popen_write_timeout(struct popen_handle *handle, const void *buf,
>   *   - count: buffer is too big.
>   *   - flags: stdout and stdrr are both choosen or both missed
>   *   - handle: handle does not support the requested IO operation.
> + *   - handle: attempt to operate on a closed fd.
>   * - SocketError: an IO error occurs at read().
>   * - TimedOut: @a timeout quota is exceeded.
>   * - FiberIsCancelled: cancelled by an outside code.
> @@ -390,12 +436,12 @@ popen_read_timeout(struct popen_handle *handle, void *buf,
>  		return -1;
>  	}
>  
> -	if (popen_may_io(handle, flags) != 0)
> -		return -1;
> -
>  	int idx = flags & POPEN_FLAG_FD_STDOUT ?
>  		STDOUT_FILENO : STDERR_FILENO;
>  
> +	if (popen_may_io(handle, idx, flags, false) != 0)
> +		return -1;
> +
>  	say_debug("popen: %d: read idx [%s:%d] buf %p count %zu "
>  		  "fds %d timeout %.9g",
>  		  handle->pid, stdX_str(idx), idx, buf, count,
> @@ -405,6 +451,80 @@ popen_read_timeout(struct popen_handle *handle, void *buf,
>  					    timeout);
>  }
...
> +int
> +popen_shutdown(struct popen_handle *handle, unsigned int flags)
> +{
> +	assert(handle != NULL);
> +
> +	if ((flags & (POPEN_FLAG_FD_STDIN |
> +		      POPEN_FLAG_FD_STDOUT |
> +		      POPEN_FLAG_FD_STDERR)) == 0) {
> +		diag_set(IllegalParams,
> +			 "popen: neither stdin, stdout nor stderr is choosen");
> +		return -1;
> +	}
> +
> +	/* Verify the operation. */
> +	for (int idx = STDIN_FILENO; idx < POPEN_FLAG_FD_STDEND_BIT; ++idx) {

	for (size_t i = 0; i < lengthof(pfd_map); i++)

We already do a build time check for STDIN_x proper mapping to numbers,
lets make it shorter.


> +		/* Operate only on asked fds. */
> +		unsigned int op_mask = pfd_map[idx].mask;
> +		if ((flags & op_mask) == 0)
> +			continue;
> +
> +		if (popen_may_io(handle, idx, op_mask, true) != 0)
> +			return -1;
> +	}
> +
> +	/* Perform the operation. */
> +	for (int idx = STDIN_FILENO; idx < POPEN_FLAG_FD_STDEND_BIT; ++idx) {
> +		/* Operate only on asked fds. */
> +		unsigned int op_mask = pfd_map[idx].mask;
> +		if ((flags & op_mask) == 0)
> +			continue;
> +
> +		/* Skip already closed fds. */
> +		if (handle->ios[idx].fd < 0)
> +			continue;
> +
> +		say_debug("popen: %d: shutdown idx [%s:%d] fd %s",
> +			  handle->pid, stdX_str(idx), idx,
> +			  handle->ios[idx].fd);
> +		coio_close_io(loop(), &handle->ios[idx]);
> +	}

I don't get why we need two for() cycles? Also, I don't like that we
mangle popen_may_io(). The shutdown is special. Why not do something like

for (size_t idx = 0; i < lengthof(pfd_map); i++) {
	unsigned int op_mask = pfd_map[idx].mask;
	if ((flags & op_mask) == 0)
		continue;

	if (handle->ios[idx].fd < 0)
		continue;

	...
}

Can't we do something like that?

	Cyrill