fs/epoll_fd: support dup file descriptor

Signed-off-by: Jiuzhu Dong <dongjiuzhu1@xiaomi.com>

fs/vfs/fs_epoll.c

@@ -32,6 +32,7 @@
 #include <errno.h>
 #include <string.h>
 #include <debug.h>
+#include <semaphore.h>
 
 #include <nuttx/clock.h>
 #include <nuttx/fs/fs.h>
@@ -47,6 +48,8 @@ struct epoll_head
 {
   int size;
   int occupied;
+  int crefs;
+  sem_t sem;
   struct file fp;
   struct inode in;
   FAR epoll_data_t *data;
@@ -57,6 +60,7 @@ struct epoll_head
  * Private Function Prototypes
  ****************************************************************************/
 
+static int epoll_do_open(FAR struct file *filep);
 static int epoll_do_close(FAR struct file *filep);
 static int epoll_do_poll(FAR struct file *filep,
                          FAR struct pollfd *fds, bool setup);
@@ -67,7 +71,7 @@ static int epoll_do_poll(FAR struct file *filep,
 
 static const struct file_operations g_epoll_ops =
 {
-  NULL,             /* open */
+  epoll_do_open,    /* open */
   epoll_do_close,   /* close */
   NULL,             /* read */
   NULL,             /* write */
@@ -108,12 +112,41 @@ static FAR struct epoll_head *epoll_head_from_fd(int fd)
   return (FAR struct epoll_head *)filep->f_inode->i_private;
 }
 
+static int epoll_do_open(FAR struct file *filep)
+{
+  FAR struct epoll_head *eph = filep->f_inode->i_private;
+  int ret;
+
+  ret = nxsem_wait(&eph->sem);
+  if (ret < 0)
+    {
+      return ret;
+    }
+
+  eph->crefs++;
+  nxsem_post(&eph->sem);
+  return ret;
+}
+
 static int epoll_do_close(FAR struct file *filep)
 {
   FAR struct epoll_head *eph = filep->f_inode->i_private;
+  int ret;
 
-  kmm_free(eph);
+  ret = nxsem_wait(&eph->sem);
-  return OK;
+  if (ret < 0)
+    {
+      return ret;
+    }
+
+  eph->crefs--;
+  nxsem_post(&eph->sem);
+  if (eph->crefs <= 0)
+    {
+      kmm_free(eph);
+    }
+
+  return ret;
 }
 
 static int epoll_do_poll(FAR struct file *filep,
@@ -138,6 +171,8 @@ static int epoll_do_create(int size, int flags)
       return -1;
     }
 
+  nxsem_init(&eph->sem, 0, 0);
+  nxsem_set_protocol(&eph->sem, SEM_PRIO_NONE);
   eph->size = size;
   eph->data = (FAR epoll_data_t *)(eph + 1);
   eph->poll = (FAR struct pollfd *)(eph->data + reserve);
@@ -155,11 +190,13 @@ static int epoll_do_create(int size, int flags)
   fd = files_allocate(&eph->in, flags, 0, eph, 0);
   if (fd < 0)
     {
+      nxsem_destroy(&eph->sem);
       kmm_free(eph);
       set_errno(-fd);
       return -1;
     }
 
+  nxsem_post(&eph->sem);
   return fd;
 }