Avoid depending on non-POSIX behavior of fcntl(2).

The POSIX standard does not say that the success return value for
fcntl(F_SETFD) and fcntl(F_SETFL) is zero; it says only that it's not -1.
We had several calls that were making the stronger assumption.  Adjust
them to test specifically for -1 for strict spec compliance.

The standard further leaves open the possibility that the O_NONBLOCK
flag bit is not the only active one in F_SETFL's argument.  Formally,
therefore, one ought to get the current flags with F_GETFL and store
them back with only the O_NONBLOCK bit changed when trying to change
the nonblock state.  In port/noblock.c, we were doing the full pushup
in pg_set_block but not in pg_set_noblock, which is just weird.  Make
both of them do it properly, since they have little business making
any assumptions about the socket they're handed.  The other places
where we're issuing F_SETFL are working with FDs we just got from
pipe(2), so it's reasonable to assume the FDs' properties are all
default, so I didn't bother adding F_GETFL steps there.

Also, while pg_set_block deserves some points for trying to do things
right, somebody had decided that it'd be even better to cast fcntl's
third argument to "long".  Which is completely loony, because POSIX
clearly says the third argument for an F_SETFL call is "int".

Given the lack of field complaints, these missteps apparently are not
of significance on any common platforms.  But they're still wrong,
so back-patch to all supported branches.

Discussion: https://postgr.es/m/30882.1492800880@sss.pgh.pa.us

diff --git a/contrib/pg_test_fsync/pg_test_fsync.c b/contrib/pg_test_fsync/pg_test_fsync.c
index 9f9c1d4d775ba40c7eb87788a7f861fe856492fc..00c74fa18423de691b1d5310ea3a4ca9e42b836b 100644 (file)
--- a/contrib/pg_test_fsync/pg_test_fsync.c
+++ b/contrib/pg_test_fsync/pg_test_fsync.c
@@ -7,6 +7,7 @@
 
 #include 
 #include 
+#include 
 #include 
 #include 
 #include 

diff --git a/src/backend/port/unix_latch.c b/src/backend/port/unix_latch.c
index 928cc441f9c0f8219a40a8b495bba93754b41b9f..b5ac6807b9e556b0c447faf6372c21bdf8db7f2b 100644 (file)
--- a/src/backend/port/unix_latch.c
+++ b/src/backend/port/unix_latch.c
@@ -89,9 +89,9 @@ InitializeLatchSupport(void)
     */
    if (pipe(pipefd) < 0)
        elog(FATAL, "pipe() failed: %m");
-   if (fcntl(pipefd[0], F_SETFL, O_NONBLOCK) < 0)
+   if (fcntl(pipefd[0], F_SETFL, O_NONBLOCK) == -1)
        elog(FATAL, "fcntl() failed on read-end of self-pipe: %m");
-   if (fcntl(pipefd[1], F_SETFL, O_NONBLOCK) < 0)
+   if (fcntl(pipefd[1], F_SETFL, O_NONBLOCK) == -1)
        elog(FATAL, "fcntl() failed on write-end of self-pipe: %m");
 
    selfpipe_readfd = pipefd[0];

diff --git a/src/backend/postmaster/postmaster.c b/src/backend/postmaster/postmaster.c
index 1dac3f0f9c447921f71a4009d51988246cf762ae..2c3c3a44e7d7fa6f0f1991527eb3b257267913ba 100644 (file)
--- a/src/backend/postmaster/postmaster.c
+++ b/src/backend/postmaster/postmaster.c
@@ -6442,7 +6442,7 @@ InitPostmasterDeathWatchHandle(void)
     * write fd. That is taken care of in ClosePostmasterPorts().
     */
    Assert(MyProcPid == PostmasterPid);
-   if (pipe(postmaster_alive_fds))
+   if (pipe(postmaster_alive_fds) < 0)
        ereport(FATAL,
                (errcode_for_file_access(),
                 errmsg_internal("could not create pipe to monitor postmaster death: %m")));
@@ -6451,7 +6451,7 @@ InitPostmasterDeathWatchHandle(void)
     * Set O_NONBLOCK to allow testing for the fd's presence with a read()
     * call.
     */
-   if (fcntl(postmaster_alive_fds[POSTMASTER_FD_WATCH], F_SETFL, O_NONBLOCK))
+   if (fcntl(postmaster_alive_fds[POSTMASTER_FD_WATCH], F_SETFL, O_NONBLOCK) == -1)
        ereport(FATAL,
                (errcode_for_socket_access(),
                 errmsg_internal("could not set postmaster death monitoring pipe to nonblocking mode: %m")));

diff --git a/src/port/noblock.c b/src/port/noblock.c
index be81d469202dc2c872360af6d13c9061f86cb28c..4e70d081557f1dd6f7e06badc8bc6b2316e4178c 100644 (file)
--- a/src/port/noblock.c
+++ b/src/port/noblock.c
@@ -1,7 +1,7 @@
 /*-------------------------------------------------------------------------
  *
  * noblock.c
- *   set a file descriptor as non-blocking
+ *   set a file descriptor as blocking or non-blocking
  *
  * Portions Copyright (c) 1996-2013, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
@@ -17,11 +17,22 @@
 #include 
 
 
+/*
+ * Put socket into nonblock mode.
+ * Returns true on success, false on failure.
+ */
 bool
 pg_set_noblock(pgsocket sock)
 {
 #if !defined(WIN32)
-   return (fcntl(sock, F_SETFL, O_NONBLOCK) != -1);
+   int         flags;
+
+   flags = fcntl(sock, F_GETFL);
+   if (flags < 0)
+       return false;
+   if (fcntl(sock, F_SETFL, (flags | O_NONBLOCK)) == -1)
+       return false;
+   return true;
 #else
    unsigned long ioctlsocket_ret = 1;
 
@@ -30,7 +41,10 @@ pg_set_noblock(pgsocket sock)
 #endif
 }
 
-
+/*
+ * Put socket into blocking mode.
+ * Returns true on success, false on failure.
+ */
 bool
 pg_set_block(pgsocket sock)
 {
@@ -38,7 +52,9 @@ pg_set_block(pgsocket sock)
    int         flags;
 
    flags = fcntl(sock, F_GETFL);
-   if (flags < 0 || fcntl(sock, F_SETFL, (long) (flags & ~O_NONBLOCK)))
+   if (flags < 0)
+       return false;
+   if (fcntl(sock, F_SETFL, (flags & ~O_NONBLOCK)) == -1)
        return false;
    return true;
 #else