From e8955cc64f0f5da0e90ab62fa3dd277a19fe3abf Mon Sep 17 00:00:00 2001
From: Michael Jeanson <mjeanson@efficios.com>
Date: Tue, 18 Apr 2023 12:11:33 -0400
Subject: [PATCH] Build fix: add a noop compat wrapper for posix_fadvise
MIME-Version: 1.0
Content-Type: text/plain; charset=utf8
Content-Transfer-Encoding: 8bit

This allows building on platforms without posix_fadvise.

Change-Id: I13fd6404cd02eb8038a97693db27d9619246401d
Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>
---
 configure.ac           |  2 +-
 src/common/io-hint.cpp | 51 +++++++++++++++++++++++++++++++++---------
 2 files changed, 41 insertions(+), 12 deletions(-)

diff --git a/configure.ac b/configure.ac
index bd6f45d5d..7257cdeff 100644
--- a/configure.ac
+++ b/configure.ac
@@ -315,7 +315,7 @@ AC_CHECK_FUNCS([ \
 	mkdir munmap putenv realpath rmdir socket strchr strcspn strdup \
 	strncasecmp strndup strnlen strpbrk strrchr strstr strtol strtoul \
 	strtoull dirfd gethostbyname2 getipnodebyname epoll_create1 \
-	sched_getcpu sysconf sync_file_range getrandom
+	sched_getcpu sysconf sync_file_range getrandom posix_fadvise
 ])
 
 # Check for pthread_setname_np and pthread_getname_np
diff --git a/src/common/io-hint.cpp b/src/common/io-hint.cpp
index 506f15de6..2bb924674 100644
--- a/src/common/io-hint.cpp
+++ b/src/common/io-hint.cpp
@@ -54,7 +54,7 @@ int flush_range_async(int fd, off_t offset, off_t nbytes)
 }
 } /* namespace */
 
-#else
+#else /* HAVE_SYNC_FILE_RANGE */
 
 namespace {
 /*
@@ -109,7 +109,44 @@ int flush_range_async(int fd, off_t offset, off_t nbytes)
 	return flush_range(fd, offset, nbytes, MS_ASYNC);
 }
 } /* namespace */
-#endif
+#endif /* !HAVE_SYNC_FILE_RANGE */
+
+/*
+ * Use posix_fadvise when available.
+ */
+#ifdef HAVE_POSIX_FADVISE
+namespace {
+int hint_dont_need(int fd, off_t offset, off_t nbytes)
+{
+	const int ret = posix_fadvise(fd, offset, nbytes, POSIX_FADV_DONTNEED);
+	if (ret && ret != -ENOSYS) {
+		PERROR("Failed to mark region as DONTNEED with posix_fadvise: fd=%i, offset=%" PRIu64
+		       ", nbytes=%" PRIu64,
+		       fd,
+		       static_cast<uint64_t>(offset),
+		       static_cast<uint64_t>(nbytes));
+		errno = ret;
+	}
+
+	return ret;
+}
+} /* namespace */
+
+#else /* HAVE_POSIX_FADVISE */
+
+/*
+ * Generic noop compat for platforms wihtout posix_fadvise, this is acceptable
+ * since we are only giving a hint to the kernel.
+ */
+namespace {
+int hint_dont_need(int fd __attribute__((unused)),
+		   off_t offset __attribute__((unused)),
+		   off_t nbytes __attribute__((unused)))
+{
+	return 0;
+}
+} /* namespace */
+#endif /* !HAVE_POSIX_FADVISE */
 
 /*
  * Give a hint to the kernel that we won't need the data at the specified range
@@ -135,15 +172,7 @@ void lttng::io::hint_flush_range_dont_need_sync(int fd, off_t offset, off_t nbyt
 	 * defined. So it can be expected to lead to lower throughput in
 	 * streaming.
 	 */
-	const int ret = posix_fadvise(fd, offset, nbytes, POSIX_FADV_DONTNEED);
-	if (ret && ret != -ENOSYS) {
-		PERROR("Failed to mark region as DONTNEED with posix_fadvise: fd=%i, offset=%" PRIu64
-		       ", nbytes=%" PRIu64,
-		       fd,
-		       static_cast<uint64_t>(offset),
-		       static_cast<uint64_t>(nbytes));
-		errno = ret;
-	}
+	hint_dont_need(fd, offset, nbytes);
 }
 
 /*
-- 
2.34.1