[PATCH v2 1/4] log: Only check for FALLOC_FL_COLLAPSE_RANGE availability at runtime

[David Gibson <david@gibson.dropbear.id.au>]

log.c has several #ifdefs on FALLOC_FL_COLLAPSE_RANGE that won't attempt
to use it if not defined.  But even if the value is defined at compile
time, it might not be available in the runtime kernel, so we need to check
for errors from a fallocate() call and fall back to other methods.

Simplify this to only need the runtime check by using linux_dep.h to define
FALLOC_FL_COLLAPSE_RANGE if it's not in the kernel headers.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
---
 Makefile    |  5 -----
 linux_dep.h |  6 ++++++
 log.c       | 10 ++--------
 3 files changed, 8 insertions(+), 13 deletions(-)

diff --git a/Makefile b/Makefile
index 3c82f50..0ba85b4 100644
--- a/Makefile
+++ b/Makefile
@@ -59,11 +59,6 @@ ifeq ($(shell :|$(CC) -fstack-protector-strong -S -xc - -o - >/dev/null 2>&1; ec
 	FLAGS += -fstack-protector-strong
 endif
 
-C := \#define _GNU_SOURCE\n\#include <fcntl.h>\nint x = FALLOC_FL_COLLAPSE_RANGE;
-ifeq ($(shell printf "$(C)" | $(CC) -S -xc - -o - >/dev/null 2>&1; echo $$?),0)
-	EXTRA_SYSCALLS += fallocate
-endif
-
 prefix		?= /usr/local
 exec_prefix	?= $(prefix)
 bindir		?= $(exec_prefix)/bin
diff --git a/linux_dep.h b/linux_dep.h
index 8921623..eae9c3c 100644
--- a/linux_dep.h
+++ b/linux_dep.h
@@ -119,4 +119,10 @@ struct tcp_info_linux {
 						 */
 };
 
+#include <linux/falloc.h>
+
+#ifndef FALLOC_FL_COLLAPSE_RANGE
+#define FALLOC_FL_COLLAPSE_RANGE	0x08
+#endif
+
 #endif /* LINUX_DEP_H */
diff --git a/log.c b/log.c
index 19f1d98..239c8ce 100644
--- a/log.c
+++ b/log.c
@@ -26,6 +26,7 @@
 #include <stdarg.h>
 #include <sys/socket.h>
 
+#include "linux_dep.h"
 #include "log.h"
 #include "util.h"
 #include "passt.h"
@@ -92,7 +93,6 @@ const char *logfile_prefix[] = {
 	"         ",		/* LOG_DEBUG */
 };
 
-#ifdef FALLOC_FL_COLLAPSE_RANGE
 /**
  * logfile_rotate_fallocate() - Write header, set log_written after fallocate()
  * @fd:		Log file descriptor
@@ -126,7 +126,6 @@ static void logfile_rotate_fallocate(int fd, const struct timespec *now)
 
 	log_written -= log_cut_size;
 }
-#endif /* FALLOC_FL_COLLAPSE_RANGE */
 
 /**
  * logfile_rotate_move() - Fallback: move recent entries toward start, then cut
@@ -198,21 +197,17 @@ out:
  *
  * Return: 0 on success, negative error code on failure
  *
- * #syscalls fcntl
- *
- * fallocate() passed as EXTRA_SYSCALL only if FALLOC_FL_COLLAPSE_RANGE is there
+ * #syscalls fcntl fallocate
  */
 static int logfile_rotate(int fd, const struct timespec *now)
 {
 	if (fcntl(fd, F_SETFL, O_RDWR /* Drop O_APPEND: explicit lseek() */))
 		return -errno;
 
-#ifdef FALLOC_FL_COLLAPSE_RANGE
 	/* Only for Linux >= 3.15, extent-based ext4 or XFS, glibc >= 2.18 */
 	if (!fallocate(fd, FALLOC_FL_COLLAPSE_RANGE, 0, log_cut_size))
 		logfile_rotate_fallocate(fd, now);
 	else
-#endif
 		logfile_rotate_move(fd, now);
 
 	if (fcntl(fd, F_SETFL, O_RDWR | O_APPEND))
@@ -432,4 +427,3 @@ void logfile_init(const char *name, const char *path, size_t size)
 	/* For FALLOC_FL_COLLAPSE_RANGE: VFS block size can be up to one page */
 	log_cut_size = ROUND_UP(log_size * LOGFILE_CUT_RATIO / 100, PAGE_SIZE);
 }
-
-- 
2.47.0