From 4cb9884ed7d3ca98ccd9bf2abbd508255b4e1fb7 Mon Sep 17 00:00:00 2001
From: DreamConnected <1487442471@qq.com>
Date: Sun, 26 Oct 2025 13:28:13 +0800
Subject: [PATCH] lxc/{terminal, file_utils}: ensure complete data writes in
 ptx/peer io handlers
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Previously, lxc_write_nointr could return without writing all data
when write() returned EAGAIN/EWOULDBLOCK due to buffer full conditions.

This change:
- Implements a loop to continue writing until all data is sent
- Handles EINTR, EAGAIN, and EWOULDBLOCK errors appropriately
- Uses poll() to wait for fd to become ready when blocked
- Maintains backward compatibility while fixing partial write issues

Signed-off-by: DreamConnected <1487442471@qq.com>
[ alex ]
- introduce a separate helper lxc_write_all and use it only in ptx/peer
  io handlers
- cleanup the code a bit
Signed-off-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@futurfusion.io>
---
 src/lxc/file_utils.c | 86 ++++++++++++++++++++++++++++++++++++++++++++
 src/lxc/file_utils.h |  2 ++
 src/lxc/terminal.c   |  4 +--
 3 files changed, 90 insertions(+), 2 deletions(-)

diff --git a/src/lxc/file_utils.c b/src/lxc/file_utils.c
index e8bf9321b..ea54939f3 100644
--- a/src/lxc/file_utils.c
+++ b/src/lxc/file_utils.c
@@ -11,6 +11,7 @@
 #include <sys/stat.h>
 #include <sys/types.h>
 #include <time.h>
+#include <poll.h>
 
 #include "file_utils.h"
 #include "macro.h"
@@ -147,6 +148,91 @@ ssize_t lxc_read_try_buf_at(int dfd, const char *path, void *buf, size_t count)
 	return ret;
 }
 
+static int __lxc_wait_for_io_ready(int fd, int event, int timeout_ms)
+{
+	int ret;
+	struct pollfd pfd = {
+		.fd = fd,
+		.events = event,
+		.revents = 0
+	};
+
+	do {
+		ret = poll(&pfd, 1, timeout_ms);
+	} while (ret < 0 && errno == EINTR);
+
+	if (ret < 0)
+		return -errno;
+
+	if (ret == 0)
+		return -ETIMEDOUT;
+
+	if (pfd.revents & (POLLERR | POLLHUP | POLLNVAL)) {
+		if (pfd.revents & POLLERR)
+			return -EPIPE;
+		if (pfd.revents & POLLHUP)
+			return -EPIPE;
+		if (pfd.revents & POLLNVAL)
+			return -EBADF;
+	}
+
+	if (!(pfd.revents & event))
+		return -EAGAIN;
+
+	return ret;
+}
+
+ssize_t lxc_write_all(int fd, const void *buf, size_t count)
+{
+	ssize_t left_to_write = count;
+	const char *ptr = buf;
+	int flags;
+
+	flags = fcntl(fd, F_GETFL);
+	if (flags < 0)
+		return ret_set_errno(-1, errno);
+
+	/* only non-blocking fds are allowed */
+	if (!(flags & O_NONBLOCK))
+		return ret_set_errno(-1, EINVAL);
+
+	while (left_to_write > 0) {
+		int ret = write(fd, ptr, left_to_write);
+
+		if (ret > 0) {
+			left_to_write -= ret;
+			ptr += ret;
+			continue;
+		}
+
+		if (ret == 0)
+			break;
+
+		/* ret < 0 */
+		if (errno == EINTR)
+			continue;
+
+		if (errno == EAGAIN) {
+			int pret = __lxc_wait_for_io_ready(fd, POLLOUT, 5000);
+
+			/* we've got an event on fd */
+			if (pret > 0)
+				continue;
+
+			if (pret == -ETIMEDOUT)
+				break;
+
+			if (pret < 0)
+				return ret_set_errno(-1, -pret);
+		}
+
+		/* some other error */
+		return ret_set_errno(-1, errno);
+	}
+
+	return count - left_to_write;
+}
+
 ssize_t lxc_write_nointr(int fd, const void *buf, size_t count)
 {
 	ssize_t ret;
diff --git a/src/lxc/file_utils.h b/src/lxc/file_utils.h
index 4fcaa4785..7d277dad3 100644
--- a/src/lxc/file_utils.h
+++ b/src/lxc/file_utils.h
@@ -35,6 +35,8 @@ __hidden extern int lxc_read_from_file(const char *filename, void *buf, size_t c
     __access_w(2, 3);
 
 /* send and receive buffers completely */
+__hidden extern ssize_t lxc_write_all(int fd, const void *buf, size_t count) __access_r(2, 3);
+
 __hidden extern ssize_t lxc_write_nointr(int fd, const void *buf, size_t count) __access_r(2, 3);
 
 __hidden extern ssize_t lxc_pwrite_nointr(int fd, const void *buf, size_t count, off_t offset)
diff --git a/src/lxc/terminal.c b/src/lxc/terminal.c
index 86fe785b6..d066c2b9e 100644
--- a/src/lxc/terminal.c
+++ b/src/lxc/terminal.c
@@ -338,7 +338,7 @@ static int lxc_terminal_ptx_io(struct lxc_terminal *terminal)
 	w_rbuf = w_log = 0;
 	/* write to peer first */
 	if (terminal->peer >= 0)
-		w = lxc_write_nointr(terminal->peer, buf, r);
+		w = lxc_write_all(terminal->peer, buf, r);
 
 	/* write to terminal ringbuffer */
 	if (terminal->buffer_size > 0)
@@ -375,7 +375,7 @@ static int lxc_terminal_peer_io(struct lxc_terminal *terminal)
 		return -1;
 	}
 
-	w = lxc_write_nointr(terminal->ptx, buf, r);
+	w = lxc_write_all(terminal->ptx, buf, r);
 	if (w != r)
 		WARN("Short write on terminal r:%d != w:%d", r, w);
 
-- 
2.47.3