unix.c: use posix_fallocate()

Using of posix_fallocate() guarantees that, if it succeed, the
attempting to write to allocated space range does not fail because of
lack of storage space. This prevents SIGBUS when trying to write to
mmaped file and no space left.

Co-Authored-by: Ivan Zakharyaschev <[email protected]>
Reported-by: Mikhail Kulagin <m.kulagin at postgrespro dot ru>

configure.ac

@@ -259,7 +259,7 @@ AC_FUNC_CHOWN
 AC_FUNC_FORK
 AC_FUNC_MMAP
 AC_FUNC_STRERROR_R
-AC_CHECK_FUNCS([alarm fsync fdatasync ftruncate \
+AC_CHECK_FUNCS([alarm fsync fdatasync ftruncate posix_fallocate \
 		gettimeofday localtime localtime_r \
 		memset munmap socket \
 		strchr strrchr strdup strstr strcasecmp \

lib/unix.c

@@ -26,6 +26,9 @@
 #ifdef HAVE_SYS_MMAN_H
 #include <sys/mman.h>
 #endif
+#if defined(HAVE_FCNTL_H) && defined(HAVE_POSIX_FALLOCATE)
+#include <fcntl.h>
+#endif
 
 #include "util_int.h"
 #include <qb/qbdefs.h>
@@ -106,12 +109,22 @@ qb_sys_mmap_file_open(char *path, const char *file, size_t bytes,
 		return res;
 	}
 
+#ifdef HAVE_POSIX_FALLOCATE
+	if ((res = posix_fallocate(fd, 0, bytes)) != 0) {
+		errno = res;
+		res = -1 * res;
+		qb_util_perror(LOG_ERR, "couldn't allocate file %s", path);
+		goto unlink_exit;
+	}
+#endif /* HAVE_POSIX_FALLOCATE */
+
 	if (ftruncate(fd, bytes) == -1) {
 		res = -errno;
 		qb_util_perror(LOG_ERR, "couldn't truncate file %s", path);
 		goto unlink_exit;
 	}
 
+#ifndef HAVE_POSIX_FALLOCATE
 	if (file_flags & O_CREAT) {
 		long page_size = sysconf(_SC_PAGESIZE);
 		long write_size = QB_MIN(page_size, bytes);
@@ -138,6 +151,7 @@ qb_sys_mmap_file_open(char *path, const char *file, size_t bytes,
 		}
 		free(buffer);
 	}
+#endif /* HAVE_POSIX_FALLOCATE */
 
 	return fd;