os: Add NotifyFd interfaces

This provides a callback-based interface to monitor file
descriptors beyond the usual client and device interfaces.

Modules within the server using file descriptors for reading and/or
writing can call

    Bool SetNotifyFd(int fd, NotifyFdProcPtr notify_fd, int mask, void *data);

mask can be any combination of X_NOTIFY_READ and X_NOTIFY_WRITE.

When 'fd' becomes readable or writable, the notify_fd function will be
called with the 'fd', the ready conditions and 'data' values as arguments,

When the module no longer needs to monitor the fd, it will call

    void RemoveNotifyFd(int fd);

RemoveNotifyFd may be called from the notify function.

Reviewed-by: Adam Jackson <ajax@redhat.com>
Signed-off-by: Keith Packard <keithp@keithp.com>

4 files changed, 103 insertions, 0 deletions

diff --git a/os/WaitFor.c b/os/WaitFor.c
index 732543086..12b21bb21 100644
--- a/os/WaitFor.c
+++ b/os/WaitFor.c
@@ -306,6 +306,10 @@ WaitForSomething(int *pClientsReady)
                 QueueWorkProc(EstablishNewConnections, NULL,
                               (void *) &LastSelectMask);
 
+            XFD_ANDSET(&tmp_set, &LastSelectMask, &NotifyReadFds);
+            if (XFD_ANYSET(&tmp_set))
+                HandleNotifyFds();
+
             if (XFD_ANYSET(&devicesReadable) || XFD_ANYSET(&clientsReadable))
                 break;
             /* check here for DDXes that queue events during Block/Wakeup */
diff --git a/os/connection.c b/os/connection.c
index 3d33c4170..0df439189 100644
--- a/os/connection.c
+++ b/os/connection.c
@@ -123,6 +123,7 @@ static int lastfdesc;           /* maximum file descriptor */
 
 fd_set WellKnownConnections;    /* Listener mask */
 fd_set EnabledDevices;          /* mask for input devices that are on */
+fd_set NotifyReadFds;           /* mask for other file descriptors */
 fd_set AllSockets;              /* select on this */
 fd_set AllClients;              /* available clients */
 fd_set LastSelectMask;          /* mask returned from last select call */
@@ -1090,6 +1091,98 @@ RemoveEnabledDevice(int fd)
     RemoveGeneralSocket(fd);
 }
 
+struct notify_fd {
+    struct xorg_list list;
+    int fd;
+    int mask;
+    NotifyFdProcPtr notify;
+    void *data;
+};
+
+static struct xorg_list notify_fds;
+
+void
+InitNotifyFds(void)
+{
+    struct notify_fd *s, *next;
+    static int been_here;
+
+    if (been_here)
+        xorg_list_for_each_entry_safe(s, next, &notify_fds, list)
+            RemoveNotifyFd(s->fd);
+
+    xorg_list_init(&notify_fds);
+    been_here = 1;
+}
+
+/*****************
+ * SetNotifyFd
+ *    Registers a callback to be invoked when the specified
+ *    file descriptor becomes readable.
+ *****************/
+
+Bool
+SetNotifyFd(int fd, NotifyFdProcPtr notify, int mask, void *data)
+{
+    struct notify_fd *n;
+    int changes;
+
+    xorg_list_for_each_entry(n, &notify_fds, list)
+        if (n->fd == fd)
+            break;
+
+    if (&n->list == &notify_fds) {
+        if (mask == 0)
+            return TRUE;
+
+        n = calloc(1, sizeof (struct notify_fd));
+        if (!n)
+            return FALSE;
+        n->fd = fd;
+        xorg_list_add(&n->list, &notify_fds);
+    }
+
+    changes = n->mask ^ mask;
+
+    if (changes & X_NOTIFY_READ) {
+        if (mask & X_NOTIFY_READ) {
+            FD_SET(fd, &NotifyReadFds);
+            AddGeneralSocket(fd);
+        } else {
+            RemoveGeneralSocket(fd);
+            FD_CLR(fd, &NotifyReadFds);
+        }
+    }
+    if (mask == 0) {
+        xorg_list_del(&n->list);
+        free(n);
+    } else {
+        n->mask = mask;
+        n->data = data;
+        n->notify = notify;
+    }
+
+    return TRUE;
+}
+
+/*****************
+ * HandlNotifyFds
+ *    A WorkProc to be called when any of the registered
+ *    file descriptors are readable.
+ *****************/
+
+void
+HandleNotifyFds(void)
+{
+    struct notify_fd *s, *next;
+
+    xorg_list_for_each_entry_safe(s, next, &notify_fds, list) {
+        if (FD_ISSET(s->fd, &LastSelectMask)) {
+            s->notify(s->fd, X_NOTIFY_READ, s->data);
+        }
+    }
+}
+
 /*****************
  * OnlyListenToOneClient:
  *    Only accept requests from  one client.  Continue to handle new
diff --git a/os/osdep.h b/os/osdep.h
index 86263a53e..2bfc783f0 100644
--- a/os/osdep.h
+++ b/os/osdep.h
@@ -159,6 +159,10 @@ extern int FlushClient(ClientPtr /*who */ ,
 extern void FreeOsBuffers(OsCommPtr     /*oc */
     );
 
+extern void InitNotifyFds(void);
+
+extern void HandleNotifyFds(void);
+
 #include "dix.h"
 
 extern fd_set AllSockets;
@@ -166,6 +170,7 @@ extern fd_set AllClients;
 extern fd_set LastSelectMask;
 extern fd_set WellKnownConnections;
 extern fd_set EnabledDevices;
+extern fd_set NotifyReadFds;
 extern fd_set ClientsWithInput;
 extern fd_set ClientsWriteBlocked;
 extern fd_set OutputPending;
diff --git a/os/osinit.c b/os/osinit.c
index 6ec2f1167..54b39a0e8 100644
--- a/os/osinit.c
+++ b/os/osinit.c
@@ -314,6 +314,7 @@ OsInit(void)
         LockServer();
         been_here = TRUE;
     }
+    InitNotifyFds();
     TimerInit();
     OsVendorInit();
     OsResetSignals();