From 560d88cb5a16636acb0e350d6997fe915cc4253e Mon Sep 17 00:00:00 2001
From: Kyle Walker <kwalker@redhat.com>
Date: Wed, 30 Jan 2019 07:50:55 -0500
Subject: [PATCH] sadc: Add a -f flag to force fdatasync() use

For quite some time, the sadc utility has not used fdatasync() when writing
stat information to disk. This resulted in instances where data files could
be corrupted or entries lost if a system encountered a sudden reset
condition. This change adds a "-f" flag which can be used to bring back the
previous behaviour if end users require it.

Note, the fdatasync() lowers the likelihood of lost data, but does so at
the expense of performance within the write operation.
---
 man/sadc.in |  8 +++++++-
 sa.h        |  2 ++
 sadc.c      | 13 ++++++++++++-
 3 files changed, 21 insertions(+), 2 deletions(-)

diff --git a/man/sadc.in b/man/sadc.in
index 2d754b71..ce8ee230 100644
--- a/man/sadc.in
+++ b/man/sadc.in
@@ -4,7 +4,7 @@ sadc \- System activity data collector.
 .SH SYNOPSIS
 .B @SA_LIB_DIR@/sadc [ -C
 .I comment
-.B ] [ -D ] [ -F ] [ -L ] [ -V ] [ -S { DISK | INT | IPV6 | POWER | SNMP | XDISK | ALL | XALL [,...] } ] [
+.B ] [ -D ] [ -F ] [ -L ] [ -V ] [ -f ] [ -S { DISK | INT | IPV6 | POWER | SNMP | XDISK | ALL | XALL [,...] } ] [
 .I interval
 .B [
 .I count
@@ -106,6 +106,12 @@ then it will be truncated. This may be useful for daily data files
 created by an older version of
 .B sadc
 and whose format is no longer compatible with current one.
+.IP -f
+fdatasync() will be used to ensure data is written to disk. This differs
+from the normal operation in that a sudden system reset is less likely to
+result in the saDD datafiles being corrupted. However, this is at the
+expense of performance within the sadc process as forward progress will be
+blocked while data is written to underlying disk instead of just to cache.
 .IP -L
 .B sadc
 will try to get an exclusive lock on the
diff --git a/sa.h b/sa.h
index 1cd0c3d9..d3236f7c 100644
--- a/sa.h
+++ b/sa.h
@@ -110,5 +110,6 @@
 #define S_F_HUMAN_READ		0x01000000
 #define S_F_ZERO_OMIT		0x02000000
+#define S_F_FDATASYNC		0x08000000
 
 #define WANT_SINCE_BOOT(m)		(((m) & S_F_SINCE_BOOT)   == S_F_SINCE_BOOT)
 #define WANT_SA_ROTAT(m)		(((m) & S_F_SA_ROTAT)     == S_F_SA_ROTAT)
@@ -138,5 +139,6 @@
 #define PACK_VIEWS(m)			(((m) & S_F_SVG_PACKED) == S_F_SVG_PACKED)
 #define DISPLAY_HUMAN_READ(m)		(((m) & S_F_HUMAN_READ) == S_F_HUMAN_READ)
+#define FDATASYNC(m)			(((m) & S_F_FDATASYNC)    == S_F_FDATASYNC)
 
 #define AO_F_NULL		0x00000000
 
diff --git a/sadc.c b/sadc.c
index 826f4aed..139d490a 100644
--- a/sadc.c
+++ b/sadc.c
@@ -92,7 +92,7 @@ void usage(char *progname)
 		progname);
 
 	fprintf(stderr, _("Options are:\n"
-			  "[ -C <comment> ] [ -D ] [ -F ] [ -L ] [ -V ]\n"
+			  "[ -C <comment> ] [ -D ] [ -F ] [ -L ] [ -V ] [ -f ]\n"
 			  "[ -S { INT | DISK | IPV6 | POWER | SNMP | XDISK | ALL | XALL } ]\n"));
 	exit(1);
 }
@@ -1109,6 +1109,13 @@ void rw_sa_stat_loop(long count, int stdfd, int ofd, char ofile[],
 
 		/* Flush data */
 		fflush(stdout);
+		if (FDATASYNC(flags)) {
+			/* If indicated, sync the data to media */
+			if (fdatasync(ofd) < 0) {
+				perror("fdatasync");
+				exit(4);
+			}
+		}
 
 		if (count > 0) {
 			count--;
@@ -1206,6 +1213,10 @@ int main(int argc, char **argv)
 			optz = 1;
 		}
 
+		else if (!strcmp(argv[opt], "-f")) {
+			flags |= S_F_FDATASYNC;
+		}
+
 		else if (!strcmp(argv[opt], "-C")) {
 			if (!argv[++opt]) {
 				usage(argv[0]);