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

[Alexander Turenko <alexander.turenko@tarantool.org>]

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);
 }
 
+/**
+ * Close parent's ends of std* fds.
+ *
+ * The following @a flags controls which fds should be closed:
+ *
+ *  POPEN_FLAG_FD_STDIN   close parent's end of child's stdin
+ *  POPEN_FLAG_FD_STDOUT  close parent's end of child's stdout
+ *  POPEN_FLAG_FD_STDERR  close parent's end of child's stderr
+ *
+ * The main reason to use this function is to send EOF to
+ * child's stdin. However parent's end of stdout / stderr
+ * may be closed too.
+ *
+ * The function does not fail on already closed fds (idempotence).
+ * However it fails on attempt to close the end of a pipe that was
+ * never exist. In other words, a subset of ..._FD_STD{IN,OUT,ERR}
+ * flags used at a handle creation may be used here.
+ *
+ * The function does not close any fds on a failure: either all
+ * requested fds are closed or neither of them.
+ *
+ * Returns 0 at success, otherwise -1 and set a diag.
+ *
+ * Possible errors:
+ *
+ * - IllegalParams: a parameter check fails:
+ *   - flags: neither stdid, stdout nor stderr is choosen.
+ *   - handle: handle does not support the requested IO operation
+ *             (one of fds is not piped).
+ */
+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) {
+		/* 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]);
+	}
+
+	return 0;
+}
+
 /**
  * Encode signal status into a human readable form.
  *
@@ -865,42 +985,6 @@ popen_new(struct popen_opts *opts)
 	int saved_errno;
 	size_t i;
 
-	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,
-		},
-	};
 	/*
 	 * At max we could be skipping each pipe end
 	 * plus dev/null variants and logfd
diff --git a/src/lib/core/popen.h b/src/lib/core/popen.h
index 4cdd95175..c068d5028 100644
--- a/src/lib/core/popen.h
+++ b/src/lib/core/popen.h
@@ -175,6 +175,9 @@ popen_read_timeout(struct popen_handle *handle, void *buf,
 		   size_t count, unsigned int flags,
 		   ev_tstamp timeout);
 
+extern int
+popen_shutdown(struct popen_handle *handle, unsigned int flags);
+
 extern void
 popen_state(struct popen_handle *handle, int *state, int *exit_code);
 
-- 
2.25.0