semihosting: Create semihost_sys_poll_one

This will be used for implementing the xtensa select_one
system call.  Choose "poll" over "select" so that we can
reuse Glib's g_poll constants and to avoid struct timeval.

Reviewed-by: Luc Michel <lmichel@kalray.eu>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

include/semihosting/console.h

@@ -53,4 +53,20 @@ int qemu_semihosting_console_write(void *buf, int len);
  */
 int qemu_semihosting_log_out(const char *s, int len);
 
+/*
+ * qemu_semihosting_console_block_until_ready:
+ * @cs: CPUState
+ *
+ * If no data is available we suspend the CPU and will re-execute the
+ * instruction when data is available.
+ */
+void qemu_semihosting_console_block_until_ready(CPUState *cs);
+
+/**
+ * qemu_semihosting_console_ready:
+ *
+ * Return true if characters are available for read; does not block.
+ */
+bool qemu_semihosting_console_ready(void);
+
 #endif /* SEMIHOST_CONSOLE_H */

include/semihosting/syscalls.h

@@ -69,4 +69,7 @@ void semihost_sys_system(CPUState *cs, gdb_syscall_complete_cb complete,
 void semihost_sys_gettimeofday(CPUState *cs, gdb_syscall_complete_cb complete,
                                target_ulong tv_addr, target_ulong tz_addr);
 
+void semihost_sys_poll_one(CPUState *cs, gdb_syscall_complete_cb complete,
+                           int fd, GIOCondition cond, int timeout);
+
 #endif /* SEMIHOSTING_SYSCALLS_H */

semihosting/console.c

@@ -77,10 +77,17 @@ static void console_read(void *opaque, const uint8_t *buf, int size)
     c->sleeping_cpus = NULL;
 }
 
-int qemu_semihosting_console_read(CPUState *cs, void *buf, int len)
+bool qemu_semihosting_console_ready(void)
+{
+    SemihostingConsole *c = &console;
+
+    g_assert(qemu_mutex_iothread_locked());
+    return !fifo8_is_empty(&c->fifo);
+}
+
+void qemu_semihosting_console_block_until_ready(CPUState *cs)
 {
     SemihostingConsole *c = &console;
-    int ret = 0;
 
     g_assert(qemu_mutex_iothread_locked());
 
@@ -92,6 +99,14 @@ int qemu_semihosting_console_read(CPUState *cs, void *buf, int len)
         cpu_loop_exit(cs);
         /* never returns */
     }
+}
+
+int qemu_semihosting_console_read(CPUState *cs, void *buf, int len)
+{
+    SemihostingConsole *c = &console;
+    int ret = 0;
+
+    qemu_semihosting_console_block_until_ready(cs);
 
     /* Read until buffer full or fifo exhausted. */
     do {

semihosting/syscalls.c

@@ -520,6 +520,21 @@ static void host_gettimeofday(CPUState *cs, gdb_syscall_complete_cb complete,
     unlock_user(p, tv_addr, sizeof(struct gdb_timeval));
 }
 
+#ifndef CONFIG_USER_ONLY
+static void host_poll_one(CPUState *cs, gdb_syscall_complete_cb complete,
+                          GuestFD *gf, GIOCondition cond, int timeout)
+{
+    /*
+     * Since this is only used by xtensa in system mode, and stdio is
+     * handled through GuestFDConsole, and there are no semihosting
+     * system calls for sockets and the like, that means this descriptor
+     * must be a normal file.  Normal files never block and are thus
+     * always ready.
+     */
+    complete(cs, cond & (G_IO_IN | G_IO_OUT), 0);
+}
+#endif
+
 /*
  * Static file semihosting syscall implementations.
  */
@@ -628,6 +643,34 @@ static void console_fstat(CPUState *cs, gdb_syscall_complete_cb complete,
     complete(cs, ret ? -1 : 0, ret ? -ret : 0);
 }
 
+#ifndef CONFIG_USER_ONLY
+static void console_poll_one(CPUState *cs, gdb_syscall_complete_cb complete,
+                             GuestFD *gf, GIOCondition cond, int timeout)
+{
+    /* The semihosting console does not support urgent data or errors. */
+    cond &= G_IO_IN | G_IO_OUT;
+
+    /*
+     * Since qemu_semihosting_console_write never blocks, we can
+     * consider output always ready -- leave G_IO_OUT alone.
+     * All that remains is to conditionally signal input ready.
+     * Since output ready causes an immediate return, only block
+     * for G_IO_IN alone.
+     *
+     * TODO: Implement proper timeout.  For now, only support
+     * indefinite wait or immediate poll.
+     */
+    if (cond == G_IO_IN && timeout < 0) {
+        qemu_semihosting_console_block_until_ready(cs);
+        /* We returned -- input must be ready. */
+    } else if ((cond & G_IO_IN) && !qemu_semihosting_console_ready()) {
+        cond &= ~G_IO_IN;
+    }
+
+    complete(cs, cond, 0);
+}
+#endif
+
 /*
  * Syscall entry points.
  */
@@ -906,3 +949,30 @@ void semihost_sys_gettimeofday(CPUState *cs, gdb_syscall_complete_cb complete,
         host_gettimeofday(cs, complete, tv_addr, tz_addr);
     }
 }
+
+#ifndef CONFIG_USER_ONLY
+void semihost_sys_poll_one(CPUState *cs, gdb_syscall_complete_cb complete,
+                           int fd, GIOCondition cond, int timeout)
+{
+    GuestFD *gf = get_guestfd(fd);
+
+    if (!gf) {
+        complete(cs, G_IO_NVAL, 1);
+        return;
+    }
+    switch (gf->type) {
+    case GuestFDGDB:
+        complete(cs, G_IO_NVAL, 1);
+        break;
+    case GuestFDHost:
+        host_poll_one(cs, complete, gf, cond, timeout);
+        break;
+    case GuestFDConsole:
+        console_poll_one(cs, complete, gf, cond, timeout);
+        break;
+    case GuestFDStatic:
+    default:
+        g_assert_not_reached();
+    }
+}
+#endif