Move pg_pwritev_with_retry() to src/common/file_utils.c

This commit moves pg_pwritev_with_retry(), a convenience wrapper of
pg_writev() able to handle partial writes, to common/file_utils.c so
that the frontend code is able to use it.  A first use-case targetted
for this routine is pg_basebackup and pg_receivewal, for the
zero-padding of a newly-initialized WAL segment.  This is used currently
in the backend when the GUC wal_init_zero is enabled (default).

Author: Bharath Rupireddy
Reviewed-by: Nathan Bossart, Thomas Munro
Discussion: https://postgr.es/m/CALj2ACUq7nAb7=bJNbK3yYmp-SZhJcXFR_pLk8un6XgDzDF3OA@mail.gmail.com

src/backend/storage/file/fd.c

@@ -93,7 +93,6 @@
 #include "common/pg_prng.h"
 #include "miscadmin.h"
 #include "pgstat.h"
-#include "port/pg_iovec.h"
 #include "portability/mem.h"
 #include "postmaster/startup.h"
 #include "storage/fd.h"
@@ -3738,67 +3737,3 @@ 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/common/file_utils.c

@@ -28,6 +28,7 @@
 #ifdef FRONTEND
 #include "common/logging.h"
 #endif
+#include "port/pg_iovec.h"
 
 #ifdef FRONTEND
 
@@ -460,3 +461,69 @@ get_dirent_type(const char *path,
 
 	return result;
 }
+
+/*
+ * pg_pwritev_with_retry
+ *
+ * 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/common/file_utils.h

@@ -24,6 +24,8 @@ typedef enum PGFileType
 	PGFILETYPE_LNK
 } PGFileType;
 
+struct iovec;					/* avoid including port/pg_iovec.h here */
+
 #ifdef FRONTEND
 extern int	fsync_fname(const char *fname, bool isdir);
 extern void fsync_pgdata(const char *pg_data, int serverVersion);
@@ -37,4 +39,9 @@ extern PGFileType get_dirent_type(const char *path,
 								  bool look_through_symlinks,
 								  int elevel);
 
+extern ssize_t pg_pwritev_with_retry(int fd,
+									 const struct iovec *iov,
+									 int iovcnt,
+									 off_t offset);
+
 #endif							/* FILE_UTILS_H */

src/include/storage/fd.h

@@ -51,8 +51,6 @@ typedef enum RecoveryInitSyncMethod
 	RECOVERY_INIT_SYNC_METHOD_SYNCFS
 }			RecoveryInitSyncMethod;
 
-struct iovec;					/* avoid including port/pg_iovec.h here */
-
 typedef int File;
 
 
@@ -178,10 +176,6 @@ extern int	pg_fsync_no_writethrough(int fd);
 extern int	pg_fsync_writethrough(int fd);
 extern int	pg_fdatasync(int fd);
 extern void pg_flush_data(int fd, off_t offset, off_t nbytes);
-extern ssize_t pg_pwritev_with_retry(int fd,
-									 const struct iovec *iov,
-									 int iovcnt,
-									 off_t offset);
 extern int	pg_truncate(const char *path, off_t length);
 extern void fsync_fname(const char *fname, bool isdir);
 extern int	fsync_fname_ext(const char *fname, bool isdir, bool ignore_perm, int elevel);