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

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

@@ -1,7 +1,7 @@
 /*-------------------------------------------------------------------------
  *
  * 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
  *
@@ -9,8 +9,7 @@
  *	  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
+}

src/port/pwrite.c

@@ -1,7 +1,7 @@
 /*-------------------------------------------------------------------------
  *
  * pwrite.c
- *	  Implementation of pwrite[v](2) for platforms that lack one.
+ *	  Implementation of pwrite(2) for platforms that lack one.
  *
  * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
  *
@@ -9,8 +9,7 @@
  *	  src/port/pwrite.c
  *
  * Note that this implementation changes the current file position, unlike
- * the POSIX function, so we use the name pg_pwrite().  Likewise for the
- * iovec version.
+ * the POSIX function, so we use the name pg_pwrite().
  *
  *-------------------------------------------------------------------------
  */
@@ -24,9 +23,6 @@
 #include <unistd.h>
 #endif
 
-#include "port/pg_iovec.h"
-
-#ifndef HAVE_PWRITE
 ssize_t
 pg_pwrite(int fd, const void *buf, size_t size, off_t offset)
 {
@@ -57,102 +53,3 @@ pg_pwrite(int fd, const void *buf, size_t size, off_t offset)
 	return write(fd, buf, size);
 #endif
 }
-#endif
-
-#ifndef HAVE_PWRITEV
-ssize_t
-pg_pwritev(int fd, const struct iovec *iov, int iovcnt, off_t offset)
-{
-#ifdef HAVE_WRITEV
-	if (iovcnt == 1)
-		return pg_pwrite(fd, iov[0].iov_base, iov[0].iov_len, offset);
-	if (lseek(fd, offset, SEEK_SET) < 0)
-		return -1;
-	return writev(fd, iov, iovcnt);
-#else
-	ssize_t		sum = 0;
-	ssize_t		part;
-
-	for (int i = 0; i < iovcnt; ++i)
-	{
-		part = pg_pwrite(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
-
-/*
- * 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/port/pwritev.c

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