Fix failure-to-read-man-page in commit 899bd785c.

posix_fallocate() is not quite a drop-in replacement for fallocate(),
because it is defined to return the error code as its function result,
not in "errno".  I (tgl) missed this because RHEL6's version seems
to set errno as well.  That is not the case on more modern Linuxen,
though, as per buildfarm results.

Aside from fixing the return-convention confusion, remove the test
for ENOSYS; we expect that glibc will mask that for posix_fallocate,
though it does not for fallocate.  Keep the test for EINTR, because
POSIX specifies that as a possible result, and buildfarm results
suggest that it can happen in practice.

Back-patch to 9.4, like the previous commit.

Thomas Munro

Discussion: https://postgr.es/m/1002664500.12301802.1471008223422.JavaMail.yahoo@mail.yahoo.com

diff --git a/src/backend/storage/ipc/dsm_impl.c b/src/backend/storage/ipc/dsm_impl.c
index fce6044a3d134e339fae8fae15185165f2bd4c65..1a11d21df0cad684017358ac62bd81feb4937206 100644 (file)
--- a/src/backend/storage/ipc/dsm_impl.c
+++ b/src/backend/storage/ipc/dsm_impl.c
@@ -425,17 +425,14 @@ dsm_impl_posix_resize(int fd, off_t size)
                do
                {
                        rc = posix_fallocate(fd, 0, size);
-               } while (rc == -1 && errno == EINTR);
+               } while (rc == EINTR);
 
-               if (rc != 0 && errno == ENOSYS)
-               {
-                       /*
-                        * Kernel too old (< 2.6.23).  Rather than fail, just trust that
-                        * we won't hit the problem (it typically doesn't show up without
-                        * many-GB-sized requests, anyway).
-                        */
-                       rc = 0;
-               }
+               /*
+                * The caller expects errno to be set, but posix_fallocate() doesn't
+                * set it.  Instead it returns error numbers directly.  So set errno,
+                * even though we'll also return rc to indicate success or failure.
+                */
+               errno = rc;
        }
 #endif                                                 /* HAVE_POSIX_FALLOCATE && __linux__ */