[Qemu-devel] [PATCH v2] qemu-io: check registered fds in command_loop()

[MORITA Kazutaka]

Some block drivers use an aio handler and do I/O completion routines
in it.  However, the handler is not invoked if we only do
aio_read/write, because registered fds are not checked at all.

This patch registers an aio handler of STDIO to checks whether we can
read a command without blocking, and calls qemu_aio_wait() in
command_loop().  Any other handlers can be invoked when user input is
idle.

Signed-off-by: MORITA Kazutaka <morita.kazut...@lab.ntt.co.jp>
---

It seems that the QEMU aio implementation doesn't allow to call
qemu_aio_wait() in the aio handler, so the previous patch is broken.

This patch only checks that STDIO is ready to read a line in the aio
handler, and invokes a command in command_loop().

I think this also fixes the problem which occurs in qemu-iotests.

 cmd.c |   33 ++++++++++++++++++++++++++++++---
 1 files changed, 30 insertions(+), 3 deletions(-)

diff --git a/cmd.c b/cmd.c
index 2336334..db2c9c4 100644
--- a/cmd.c
+++ b/cmd.c
@@ -24,6 +24,7 @@
 #include <getopt.h>
 
 #include "cmd.h"
+#include "qemu-aio.h"
 
 #define _(x)   x       /* not gettext support yet */
 
@@ -149,10 +150,20 @@ add_args_command(
        args_func = af;
 }
 
+static void prep_fetchline(void *opaque)
+{
+    int *fetchable = opaque;
+
+    qemu_aio_set_fd_handler(STDIN_FILENO, NULL, NULL, NULL, NULL, NULL);
+    *fetchable= 1;
+}
+
+static char *get_prompt(void);
+
 void
 command_loop(void)
 {
-       int             c, i, j = 0, done = 0;
+       int             c, i, j = 0, done = 0, fetchable = 0, prompted = 0;
        char            *input;
        char            **v;
        const cmdinfo_t *ct;
@@ -186,7 +197,21 @@ command_loop(void)
                free(cmdline);
                return;
        }
+
        while (!done) {
+        if (!prompted) {
+            printf("%s", get_prompt());
+            fflush(stdout);
+            qemu_aio_set_fd_handler(STDIN_FILENO, prep_fetchline, NULL, NULL,
+                                    NULL, &fetchable);
+            prompted = 1;
+        }
+
+        qemu_aio_wait();
+
+        if (!fetchable) {
+            continue;
+        }
                if ((input = fetchline()) == NULL)
                        break;
                v = breakline(input, &c);
@@ -199,7 +224,11 @@ command_loop(void)
                                        v[0]);
                }
                doneline(input, v);
+
+        prompted = 0;
+        fetchable = 0;
        }
+    qemu_aio_set_fd_handler(STDIN_FILENO, NULL, NULL, NULL, NULL, NULL);
 }
 
 /* from libxcmd/input.c */
@@ -270,8 +299,6 @@ fetchline(void)
 
        if (!line)
                return NULL;
-       printf("%s", get_prompt());
-       fflush(stdout);
        if (!fgets(line, MAXREADLINESZ, stdin)) {
                free(line);
                return NULL;
-- 
1.5.6.5