Move our p{read,write}v replacements into their own files.

macOS's ranlib issued a warning about an empty pread.o file with the
previous arrangement, on systems new enough to require no replacement
functions.  Let's go back to using configure's AC_REPLACE_FUNCS system
to build and include each .o in the library only if it's needed, which
requires moving the *v() functions to their own files.

Also move the _with_retry() wrapper to a more permanent home.

Reported-by: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://postgr.es/m/1283127.1610554395%40sss.pgh.pa.us

Author: macdice

configure

@@ -15155,7 +15155,7 @@ fi
 LIBS_including_readline="$LIBS"
 LIBS=`echo "$LIBS" | sed -e 's/-ledit//g' -e 's/-lreadline//g'`
 
-for ac_func in backtrace_symbols clock_gettime copyfile fdatasync getifaddrs getpeerucred getrlimit kqueue mbstowcs_l memset_s poll posix_fallocate ppoll pread preadv pstat pthread_is_threaded_np pwrite pwritev readlink readv setproctitle setproctitle_fast setsid shm_open strchrnul strsignal symlink sync_file_range uselocale wcstombs_l writev
+for ac_func in backtrace_symbols clock_gettime copyfile fdatasync getifaddrs getpeerucred getrlimit kqueue mbstowcs_l memset_s poll posix_fallocate ppoll pstat pthread_is_threaded_np readlink readv setproctitle setproctitle_fast setsid shm_open strchrnul strsignal symlink sync_file_range uselocale wcstombs_l writev
 do :
   as_ac_var=`$as_echo "ac_cv_func_$ac_func" | $as_tr_sh`
 ac_fn_c_check_func "$LINENO" "$ac_func" "$as_ac_var"
@@ -15832,6 +15832,58 @@ esac
 
 fi
 
+ac_fn_c_check_func "$LINENO" "pread" "ac_cv_func_pread"
+if test "x$ac_cv_func_pread" = xyes; then :
+  $as_echo "#define HAVE_PREAD 1" >>confdefs.h
+
+else
+  case " $LIBOBJS " in
+  *" pread.$ac_objext "* ) ;;
+  *) LIBOBJS="$LIBOBJS pread.$ac_objext"
+ ;;
+esac
+
+fi
+
+ac_fn_c_check_func "$LINENO" "preadv" "ac_cv_func_preadv"
+if test "x$ac_cv_func_preadv" = xyes; then :
+  $as_echo "#define HAVE_PREADV 1" >>confdefs.h
+
+else
+  case " $LIBOBJS " in
+  *" preadv.$ac_objext "* ) ;;
+  *) LIBOBJS="$LIBOBJS preadv.$ac_objext"
+ ;;
+esac
+
+fi
+
+ac_fn_c_check_func "$LINENO" "pwrite" "ac_cv_func_pwrite"
+if test "x$ac_cv_func_pwrite" = xyes; then :
+  $as_echo "#define HAVE_PWRITE 1" >>confdefs.h
+
+else
+  case " $LIBOBJS " in
+  *" pwrite.$ac_objext "* ) ;;
+  *) LIBOBJS="$LIBOBJS pwrite.$ac_objext"
+ ;;
+esac
+
+fi
+
+ac_fn_c_check_func "$LINENO" "pwritev" "ac_cv_func_pwritev"
+if test "x$ac_cv_func_pwritev" = xyes; then :
+  $as_echo "#define HAVE_PWRITEV 1" >>confdefs.h
+
+else
+  case " $LIBOBJS " in
+  *" pwritev.$ac_objext "* ) ;;
+  *) LIBOBJS="$LIBOBJS pwritev.$ac_objext"
+ ;;
+esac
+
+fi
+
 ac_fn_c_check_func "$LINENO" "random" "ac_cv_func_random"
 if test "x$ac_cv_func_random" = xyes; then :
   $as_echo "#define HAVE_RANDOM 1" >>confdefs.h

configure.ac

@@ -1661,12 +1661,8 @@ AC_CHECK_FUNCS(m4_normalize([
 	poll
 	posix_fallocate
 	ppoll
-	pread
-	preadv
 	pstat
 	pthread_is_threaded_np
-	pwrite
-	pwritev
 	readlink
 	readv
 	setproctitle
@@ -1740,6 +1736,10 @@ AC_REPLACE_FUNCS(m4_normalize([
 	inet_aton
 	link
 	mkdtemp
+	pread
+	preadv
+	pwrite
+	pwritev
 	random
 	srandom
 	strlcat

src/backend/storage/file/fd.c

@@ -92,6 +92,7 @@
 #include "common/file_utils.h"
 #include "miscadmin.h"
 #include "pgstat.h"
+#include "port/pg_iovec.h"
 #include "portability/mem.h"
 #include "storage/fd.h"
 #include "storage/ipc.h"
@@ -3635,3 +3636,67 @@ data_sync_elevel(int elevel)
 {
 	return data_sync_retry ? elevel : PANIC;
 }
+
+/*
+ * A convenience wrapper for pg_pwritev() that retries on partial write.  If an
+ * error is returned, it is unspecified how much has been written.
+ */
+ssize_t
+pg_pwritev_with_retry(int fd, const struct iovec *iov, int iovcnt, off_t offset)
+{
+	struct iovec iov_copy[PG_IOV_MAX];
+	ssize_t		sum = 0;
+	ssize_t		part;
+
+	/* We'd better have space to make a copy, in case we need to retry. */
+	if (iovcnt > PG_IOV_MAX)
+	{
+		errno = EINVAL;
+		return -1;
+	}
+
+	for (;;)
+	{
+		/* Write as much as we can. */
+		part = pg_pwritev(fd, iov, iovcnt, offset);
+		if (part < 0)
+			return -1;
+
+#ifdef SIMULATE_SHORT_WRITE
+		part = Min(part, 4096);
+#endif
+
+		/* Count our progress. */
+		sum += part;
+		offset += part;
+
+		/* Step over iovecs that are done. */
+		while (iovcnt > 0 && iov->iov_len <= part)
+		{
+			part -= iov->iov_len;
+			++iov;
+			--iovcnt;
+		}
+
+		/* Are they all done? */
+		if (iovcnt == 0)
+		{
+			/* We don't expect the kernel to write more than requested. */
+			Assert(part == 0);
+			break;
+		}
+
+		/*
+		 * Move whatever's left to the front of our mutable copy and adjust
+		 * the leading iovec.
+		 */
+		Assert(iovcnt > 0);
+		memmove(iov_copy, iov, sizeof(*iov) * iovcnt);
+		Assert(iov->iov_len > part);
+		iov_copy[0].iov_base = (char *) iov_copy[0].iov_base + part;
+		iov_copy[0].iov_len -= part;
+		iov = iov_copy;
+	}
+
+	return sum;
+}

src/include/storage/fd.h

@@ -45,6 +45,7 @@
 
 #include <dirent.h>
 
+struct iovec;					/* avoid including port/pg_iovec.h here */
 
 typedef int File;
 
@@ -161,6 +162,10 @@ extern int	durable_unlink(const char *fname, int loglevel);
 extern int	durable_rename_excl(const char *oldfile, const char *newfile, int loglevel);
 extern void SyncDataDirectory(void);
 extern int	data_sync_elevel(int elevel);
+extern ssize_t pg_pwritev_with_retry(int fd,
+									 const struct iovec *iov,
+									 int iovcnt,
+									 off_t offset);
 
 /* Filename components */
 #define PG_TEMP_FILES_DIR "pgsql_tmp"

src/port/Makefile

@@ -53,8 +53,6 @@ OBJS = \
 	pgstrcasecmp.o \
 	pgstrsignal.o \
 	pqsignal.o \
-	pread.o \
-	pwrite.o \
 	qsort.o \
 	qsort_arg.o \
 	quotes.o \

src/port/pread.c

@@ -1,16 +1,15 @@
 /*-------------------------------------------------------------------------
  *
  * pread.c
- *	  Implementation of pread[v](2) for platforms that lack one.
+ *	  Implementation of pread(2) for platforms that lack one.
  *
  * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
  *
  * IDENTIFICATION
  *	  src/port/pread.c
  *
  * Note that this implementation changes the current file position, unlike
- * the POSIX function, so we use the name pg_pread().  Likewise for the
- * iovec version.
+ * the POSIX function, so we use the name pg_pread().
  *
  *-------------------------------------------------------------------------
  */
@@ -24,9 +23,6 @@
 #include <unistd.h>
 #endif
 
-#include "port/pg_iovec.h"
-
-#ifndef HAVE_PREAD
 ssize_t
 pg_pread(int fd, void *buf, size_t size, off_t offset)
 {
@@ -60,38 +56,3 @@ pg_pread(int fd, void *buf, size_t size, off_t offset)
 	return read(fd, buf, size);
 #endif
 }
-#endif
-
-#ifndef HAVE_PREADV
-ssize_t
-pg_preadv(int fd, const struct iovec *iov, int iovcnt, off_t offset)
-{
-#ifdef HAVE_READV
-	if (iovcnt == 1)
-		return pg_pread(fd, iov[0].iov_base, iov[0].iov_len, offset);
-	if (lseek(fd, offset, SEEK_SET) < 0)
-		return -1;
-	return readv(fd, iov, iovcnt);
-#else
-	ssize_t 	sum = 0;
-	ssize_t 	part;
-
-	for (int i = 0; i < iovcnt; ++i)
-	{
-		part = pg_pread(fd, iov[i].iov_base, iov[i].iov_len, offset);
-		if (part < 0)
-		{
-			if (i == 0)
-				return -1;
-			else
-				return sum;
-		}
-		sum += part;
-		offset += part;
-		if (part < iov[i].iov_len)
-			return sum;
-	}
-	return sum;
-#endif
-}
-#endif

src/port/preadv.c

@@ -0,0 +1,58 @@
+/*-------------------------------------------------------------------------
+ *
+ * preadv.c
+ *	  Implementation of preadv(2) for platforms that lack one.
+ *
+ * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
+ *
+ * IDENTIFICATION
+ *	  src/port/preadv.c
+ *
+ * Note that this implementation changes the current file position, unlike
+ * the POSIX-like function, so we use the name pg_preadv().
+ *
+ *-------------------------------------------------------------------------
+ */
+
+
+#include "postgres.h"
+
+#ifdef WIN32
+#include <windows.h>
+#else
+#include <unistd.h>
+#endif
+
+#include "port/pg_iovec.h"
+
+ssize_t
+pg_preadv(int fd, const struct iovec *iov, int iovcnt, off_t offset)
+{
+#ifdef HAVE_READV
+	if (iovcnt == 1)
+		return pg_pread(fd, iov[0].iov_base, iov[0].iov_len, offset);
+	if (lseek(fd, offset, SEEK_SET) < 0)
+		return -1;
+	return readv(fd, iov, iovcnt);
+#else
+	ssize_t 	sum = 0;
+	ssize_t 	part;
+
+	for (int i = 0; i < iovcnt; ++i)
+	{
+		part = pg_pread(fd, iov[i].iov_base, iov[i].iov_len, offset);
+		if (part < 0)
+		{
+			if (i == 0)
+				return -1;
+			else
+				return sum;
+		}
+		sum += part;
+		offset += part;
+		if (part < iov[i].iov_len)
+			return sum;
+	}
+	return sum;
+#endif
+}