Make io_select return errors

instead of returning 0 and make clients have to actually read the error.
This makes implementing "poll" much easier.

Based on Svante Signell's patch.

* pflocal/io.c (S_io_select): Return error returned by pipe_wait_readable or
pipe_wait_writable.
* trans/fifo.c (trivfs_S_io_select): Return error returned by
pipe_wait_readable or pipe_wait_writable. Return EBADF on bogus access mode.
* trans/new-fifo.c (trivfs_S_io_select): Likewise.

3 files changed, 55 insertions, 16 deletions

diff --git a/pflocal/io.c b/pflocal/io.c
index f67052f3..2301611e 100644
--- a/pflocal/io.c
+++ b/pflocal/io.c
@@ -231,15 +231,24 @@ S_io_select (struct sock_user *user,
       if (valid & SELECT_READ)
 	{
 	  pipe_acquire_reader (read_pipe);
-	  if (pipe_wait_readable (read_pipe, 1, 1) != EWOULDBLOCK)
-	    ready |= SELECT_READ; /* Data immediately readable (or error). */
+	  err = pipe_wait_readable (read_pipe, 1, 1);
+	  if (err == EWOULDBLOCK)
+	    err = 0; /* Not readable, actually not an error.  */
+	  else
+	    ready |= SELECT_READ; /* Data immediately readable (or error).  */
 	  pthread_mutex_unlock (&read_pipe->lock);
+	  if (err)
+	    /* Prevent write test from overwriting err.  */
+	    valid &= ~SELECT_WRITE;
 	}
       if (valid & SELECT_WRITE)
 	{
 	  pipe_acquire_writer (write_pipe);
-	  if (pipe_wait_writable (write_pipe, 1) != EWOULDBLOCK)
-	    ready |= SELECT_WRITE; /* Data immediately writable (or error). */
+	  err = pipe_wait_writable (write_pipe, 1);
+	  if (err == EWOULDBLOCK)
+	    err = 0; /* Not writable, actually not an error.  */
+	  else
+	    ready |= SELECT_WRITE; /* Data immediately writable (or error).  */
 	  pthread_mutex_unlock (&write_pipe->lock);
 	}
 
diff --git a/trans/fifo.c b/trans/fifo.c
index 4fe999dd..b40a50d1 100644
--- a/trans/fifo.c
+++ b/trans/fifo.c
@@ -424,12 +424,21 @@ trivfs_S_io_select (struct trivfs_protid *cred,
       if (cred->po->openmodes & O_READ)
 	{
 	  pthread_mutex_lock (&pipe->lock);
-	  if (pipe_wait_readable (pipe, 1, 1) != EWOULDBLOCK)
-	    ready |= SELECT_READ; /* Data immediately readable (or error). */
+	  err = pipe_wait_readable (pipe, 1, 1);
+	  if (err == EWOULDBLOCK)
+	    err = 0; /* Not readable, actually not an error.  */
+	  else
+	    ready |= SELECT_READ; /* Data immediately readable (or error).  */
 	  pthread_mutex_unlock (&pipe->lock);
 	}
       else
-	ready |= SELECT_READ;	/* Error immediately available...  */
+	{
+	  err = EBADF;
+	  ready |= SELECT_READ;	/* Error immediately available...  */
+	}
+      if (err)
+	/* Prevent write test from overwriting err.  */
+	*select_type &= ~SELECT_WRITE;
     }
 
   if (*select_type & SELECT_WRITE)
@@ -437,12 +446,18 @@ trivfs_S_io_select (struct trivfs_protid *cred,
       if (cred->po->openmodes & O_WRITE)
 	{
 	  pthread_mutex_lock (&pipe->lock);
-	  if (pipe_wait_writable (pipe, 1) != EWOULDBLOCK)
-	    ready |= SELECT_WRITE; /* Data immediately writable (or error). */
+	  err = pipe_wait_writable (pipe, 1);
+	  if (err == EWOULDBLOCK)
+	    err = 0; /* Not writable, actually not an error.  */
+	  else
+	    ready |= SELECT_WRITE; /* Data immediately writable (or error).  */
 	  pthread_mutex_unlock (&pipe->lock);
 	}
       else
-	ready |= SELECT_WRITE;	/* Error immediately available...  */
+	{
+	  err = EBADF;
+	  ready |= SELECT_WRITE;	/* Error immediately available...  */
+	}
     }
 
   if (ready)
diff --git a/trans/new-fifo.c b/trans/new-fifo.c
index cc16b988..5cc44b58 100644
--- a/trans/new-fifo.c
+++ b/trans/new-fifo.c
@@ -610,12 +610,21 @@ trivfs_S_io_select (struct trivfs_protid *cred,
       if (cred->po->openmodes & O_READ)
 	{
 	  pthread_mutex_lock (&pipe->lock);
-	  if (pipe_wait_readable (pipe, 1, 1) != EWOULDBLOCK)
-	    ready |= SELECT_READ; /* Data immediately readable (or error). */
+	  err = pipe_wait_readable (pipe, 1, 1);
+	  if (err == EWOULDBLOCK)
+	    err = 0; /* Not readable, actually not an error.  */
+	  else
+	    ready |= SELECT_READ; /* Data immediately readable (or error).  */
 	  pthread_mutex_unlock (&pipe->lock);
 	}
       else
-	ready |= SELECT_READ;	/* Error immediately available...  */
+	{
+	  err = EBADF;
+	  ready |= SELECT_READ;	/* Error immediately available...  */
+	}
+      if (err)
+	/* Prevent write test from overwriting err.  */
+	*select_type &= ~SELECT_WRITE;
     }
 
   if (*select_type & SELECT_WRITE)
@@ -623,12 +632,18 @@ trivfs_S_io_select (struct trivfs_protid *cred,
       if (cred->po->openmodes & O_WRITE)
 	{
 	  pthread_mutex_lock (&pipe->lock);
-	  if (pipe_wait_writable (pipe, 1) != EWOULDBLOCK)
-	    ready |= SELECT_WRITE; /* Data immediately writable (or error). */
+	  err = pipe_wait_writable (pipe, 1);
+	  if (err == EWOULDBLOCK)
+	    err = 0; /* Not writable, actually not an error.  */
+	  else
+	    ready |= SELECT_WRITE; /* Data immediately writable (or error).  */
 	  pthread_mutex_unlock (&pipe->lock);
 	}
       else
-	ready |= SELECT_WRITE;	/* Error immediately available...  */
+	{
+	  err = EBADF;
+	  ready |= SELECT_WRITE;	/* Error immediately available...  */
+	}
     }
 
   if (ready)