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/src/backend/postmaster/postmaster.c b/src/backend/postmaster/postmaster.c
index 533252a25888afc19366aaed5913729c0f0d9551..218915f3be76c1a46af8caf75b09cf55808adc52 100644 (file)
--- a/src/backend/postmaster/postmaster.c
+++ b/src/backend/postmaster/postmaster.c
@@ -6214,7 +6214,7 @@ 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")));
@@ -6223,7 +6223,7 @@ 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/backend/storage/ipc/latch.c b/src/backend/storage/ipc/latch.c
index 3e0c4689db549e2d502589b8194bee4e60f4c316..cac72ae4283dd8451820c9d45f2d454f6be9d910 100644 (file)
--- a/src/backend/storage/ipc/latch.c
+++ b/src/backend/storage/ipc/latch.c
@@ -169,9 +169,9 @@ 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/bin/pg_test_fsync/pg_test_fsync.c b/src/bin/pg_test_fsync/pg_test_fsync.c
index c8427623d20bc0275111c4ba0b0f70c959d7d636..b4f3551b94a61f09f93ac66054a495532993da7a 100644 (file)
--- a/src/bin/pg_test_fsync/pg_test_fsync.c
+++ b/src/bin/pg_test_fsync/pg_test_fsync.c
@@ -7,6 +7,7 @@
 
 #include 
 #include 
+#include 
 #include 
 #include 
 #include 

diff --git a/src/port/noblock.c b/src/port/noblock.c
index 52e1d71d9d25c8d0cb9b3ac7c67a5981b94760a1..959d3ada86b9a1c3907b5be643a85ab27ab2c3be 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) 1996-2016, 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