Re: [Qemu-devel] [PATCH 2/3] Always use nonblocking mode for qemu_chr_open_fd.

[Kevin Wolf <kwolf@suse.de>]

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Anthony Liguori schrieb:
> This changes semantics a bit.  Previously, using a pty would guarantee
> that data is always written as qemu_chr_write does not perform any sort
> of buffering.
> 
> Now, that data will be silently dropped instead of causing QEMU to
> block.  I don't think it's perfectly clear that one behaviour is clearly
> better than the other.

Then we need both.

Add an option to specify non-blocking mode for stdio, pty and pipe in
qemu_chr_open.  Blocking mode is used by default (maintaining current
semantics), non-blocking mode if the name is prefixed with nonblock:

Signed-off-by: Kevin Wolf <kwolf@suse.de>

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Index: vl.c
===================================================================
--- vl.c.orig
+++ vl.c
@@ -2227,11 +2227,16 @@ static void fd_chr_close(struct CharDriv
 }
 
 /* open a character device to a unix fd */
-static CharDriverState *qemu_chr_open_fd(int fd_in, int fd_out)
+static CharDriverState *qemu_chr_open_fd(int fd_in, int fd_out, int block)
 {
     CharDriverState *chr;
     FDCharDriver *s;
 
+    if (!block) {
+        socket_set_nonblock(fd_in);
+        socket_set_nonblock(fd_out);
+    }
+
     chr = qemu_mallocz(sizeof(CharDriverState));
     if (!chr)
         return NULL;
@@ -2259,10 +2264,10 @@ static CharDriverState *qemu_chr_open_fi
     TFR(fd_out = open(file_out, O_WRONLY | O_TRUNC | O_CREAT | O_BINARY, 0666));
     if (fd_out < 0)
         return NULL;
-    return qemu_chr_open_fd(-1, fd_out);
+    return qemu_chr_open_fd(-1, fd_out, 0);
 }
 
-static CharDriverState *qemu_chr_open_pipe(const char *filename)
+static CharDriverState *qemu_chr_open_pipe(const char *filename, int block)
 {
     int fd_in, fd_out;
     char filename_in[256], filename_out[256];
@@ -2280,7 +2285,7 @@ static CharDriverState *qemu_chr_open_pi
         if (fd_in < 0)
             return NULL;
     }
-    return qemu_chr_open_fd(fd_in, fd_out);
+    return qemu_chr_open_fd(fd_in, fd_out, block);
 }
 
 
@@ -2376,13 +2381,13 @@ static void qemu_chr_close_stdio(struct
     fd_chr_close(chr);
 }
 
-static CharDriverState *qemu_chr_open_stdio(void)
+static CharDriverState *qemu_chr_open_stdio(int block)
 {
     CharDriverState *chr;
 
     if (stdio_nb_clients >= STDIO_MAX_CLIENTS)
         return NULL;
-    chr = qemu_chr_open_fd(0, 1);
+    chr = qemu_chr_open_fd(0, 1, block);
     chr->chr_close = qemu_chr_close_stdio;
     qemu_set_fd_handler2(0, stdio_read_poll, stdio_read, NULL, chr);
     stdio_nb_clients++;
@@ -2449,7 +2454,7 @@ void cfmakeraw (struct termios *termios_
 #endif
 
 #if defined(__linux__) || defined(__sun__)
-static CharDriverState *qemu_chr_open_pty(void)
+static CharDriverState *qemu_chr_open_pty(int block)
 {
     struct termios tty;
     int master_fd, slave_fd;
@@ -2463,7 +2468,7 @@ static CharDriverState *qemu_chr_open_pt
     tcsetattr(slave_fd, TCSAFLUSH, &tty);
 
     fprintf(stderr, "char device redirected to %s\n", ptsname(master_fd));
-    return qemu_chr_open_fd(master_fd, master_fd);
+    return qemu_chr_open_fd(master_fd, master_fd, block);
 }
 
 static void tty_serial_init(int fd, int speed,
@@ -2578,7 +2583,7 @@ static CharDriverState *qemu_chr_open_tt
 
     TFR(fd = open(filename, O_RDWR | O_NONBLOCK));
     tty_serial_init(fd, 115200, 'N', 8, 1);
-    chr = qemu_chr_open_fd(fd, fd);
+    chr = qemu_chr_open_fd(fd, fd, 0);
     if (!chr) {
         close(fd);
         return NULL;
@@ -2588,7 +2593,7 @@ static CharDriverState *qemu_chr_open_tt
     return chr;
 }
 #else  /* ! __linux__ && ! __sun__ */
-static CharDriverState *qemu_chr_open_pty(void)
+static CharDriverState *qemu_chr_open_pty(int block)
 {
     return NULL;
 }
@@ -3582,6 +3587,10 @@ static CharDriverState *qemu_chr_open_tc
 CharDriverState *qemu_chr_open(const char *filename)
 {
     const char *p;
+    int block = 1;
+
+    if (strstart(filename, "nonblock:", &filename))
+        block = 0;
 
     if (!strcmp(filename, "vc")) {
         return text_console_init(&display_state, 0);
@@ -3615,11 +3624,11 @@ CharDriverState *qemu_chr_open(const cha
     } else if (strstart(filename, "file:", &p)) {
         return qemu_chr_open_file_out(p);
     } else if (strstart(filename, "pipe:", &p)) {
-        return qemu_chr_open_pipe(p);
+        return qemu_chr_open_pipe(p, block);
     } else if (!strcmp(filename, "pty")) {
-        return qemu_chr_open_pty();
+        return qemu_chr_open_pty(block);
     } else if (!strcmp(filename, "stdio")) {
-        return qemu_chr_open_stdio();
+        return qemu_chr_open_stdio(block);
     } else
 #if defined(__linux__)
     if (strstart(filename, "/dev/parport", NULL)) {