New feature: Niceness: change nice and ionice level of the local and/or remote process using the --nice option

.gitignore

@@ -60,3 +60,11 @@ aclocal.m4
 .deps
 /*.exe
 *.dSYM/
+simdtest
+t_chmod_secure
+t_secure_relpath
+testsuite/__pycache__/
+testsuite/chown-fake_test.py
+testsuite/devices-fake_test.py
+testsuite/exclude-lsh_test.py
+testsuite/xattrs-hlink_test.py

Makefile.in

@@ -51,7 +51,8 @@ OBJS3=progress.o pipe.o @MD5_ASM@ @ROLL_SIMD@ @ROLL_ASM@
 DAEMON_OBJ = params.o loadparm.o clientserver.o access.o connection.o authenticate.o
 popt_OBJS= popt/popt.o  popt/poptconfig.o \
 	popt/popthelp.o popt/poptparse.o popt/poptint.o
-OBJS=$(OBJS1) $(OBJS2) $(OBJS3) $(DAEMON_OBJ) $(LIBOBJ) @BUILD_ZLIB@ @BUILD_POPT@
+NICENESS_OBJS = niceness/ionice_string.o niceness/niceness.o niceness/niceness_syscall.o niceness/parse_arguments.o
+OBJS=$(OBJS1) $(OBJS2) $(OBJS3) $(DAEMON_OBJ) $(NICENESS_OBJS) $(LIBOBJ) @BUILD_ZLIB@ @BUILD_POPT@
 
 TLS_OBJ = tls.o syscall.o android.o util2.o t_stub.o lib/compat.o lib/snprintf.o lib/permstring.o lib/sysxattrs.o @BUILD_POPT@
 

configure.ac

@@ -13,7 +13,7 @@ AC_CHECK_HEADERS(sys/fcntl.h sys/select.h fcntl.h sys/time.h sys/unistd.h \
     sys/acl.h acl/libacl.h attr/xattr.h sys/xattr.h sys/extattr.h dl.h \
     popt.h popt/popt.h linux/falloc.h netinet/in_systm.h netgroup.h \
     zlib.h xxhash.h openssl/md4.h openssl/md5.h zstd.h lz4.h sys/file.h \
-    bsd/string.h)
+    bsd/string.h sys/resource.h linux/ioprio.h sys/syscall.h)
 AC_CHECK_HEADERS([netinet/ip.h], [], [], [[#include <netinet/in.h>]])
 AC_HEADER_MAJOR_FIXED
 
@@ -1479,6 +1479,8 @@ case "$CC" in
     ;;
 esac
 
+AC_DEFINE_UNQUOTED([COMPILE_TARGET], ["$host"], [String describing the compiled target OS and architecture])
+
 AC_CONFIG_FILES([Makefile lib/dummy zlib/dummy popt/dummy shconfig])
 AC_OUTPUT
 

main.c

@@ -1844,6 +1844,8 @@ int main(int argc,char *argv[])
 	if (write_batch < 0)
 		dry_run = 1;
 
+	niceness_renice_and_ionice_me();
+
 	if (am_server) {
 #ifdef ICONV_CONST
 		setup_iconv();

niceness/ionice_string.c

@@ -0,0 +1,49 @@
+/*
+ * Renice or ionice the rsync process to reduce its impact on the system
+ * ionice_string.c - string conversion utilities for ionice
+ *
+ * Copyright (C) 2026 Michael Mess
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, visit the http://fsf.org website.
+ */
+
+#include <strings.h>
+#include "niceness.h"
+
+/*
+ * Get the string representation for the given ionice_value
+ */
+const char *intToIoniceValueString(int ionice_value)
+{
+	if (ionice_value<-8) return 0;
+	if (ionice_value>9) return 0;
+	return Ionice_ValueStrings[ionice_value+8];
+}
+
+/*
+ * Parse string into ionice_value. Returns 1 on success, 0 otherwise.
+ */
+int ioniceStringToInt(char * string, int *ionice_value)
+{
+	for (int i=0; Ionice_ValueStrings[i]; i++)
+	{
+		if (strncasecmp(string, Ionice_ValueStrings[i], 4) == 0) // All values are 4 chars long
+		{
+			*ionice_value=i-8;
+			return 1;
+		}
+	}
+	return 0;
+}
+

niceness/ionice_string.h

@@ -0,0 +1,31 @@
+/*
+ * Renice or ionice the rsync process to reduce its impact on the system
+ * ionice_string.h - string conversion utilities for ionice
+ *
+ * Copyright (C) 2026 Michael Mess
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, visit the http://fsf.org website.
+ */
+
+#include "niceness.h"
+
+/*
+ * Get the string representation for the given ionice_value
+ */
+const char *intToIoniceValueString(int ionice_value);
+
+/*
+ * Parse string into ionice_value. Returns 1 on success, 0 otherwise.
+ */
+int ioniceStringToInt(char * string, int *ionice_value);

niceness/niceness.c

@@ -0,0 +1,98 @@
+/*
+ * Renice or ionice the rsync process to reduce its impact on the system
+ * niceness.c - core niceness state holder
+ *
+ * Copyright (C) 2026 Michael Mess
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, visit the http://fsf.org website.
+ */
+
+#include "niceness.h"
+
+/*
+ * String representation of ionice. All strings have to be 4 characters long.
+ */
+const char *Ionice_ValueStrings[] = {
+	"rt_0",
+	"rt_1",
+	"rt_2",
+	"rt_3",
+	"rt_4",
+	"rt_5",
+	"rt_6",
+	"rt_7",
+	"none",
+	"be_0",
+	"be_1",
+	"be_2",
+	"be_3",
+	"be_4",
+	"be_5",
+	"be_6",
+	"be_7",
+	"idle",
+	0
+};
+
+struct niceness niceness = {
+	/* If set to other than 0, be nice on the local or remote site
+	 * Contains the nice priority to be set on the process, or 0=feature is turned off, no priority will be set.
+	 * I have to admit, that it is not possible to set a nice value of 0 with this code,
+	 * but in most cases 0 should be the priority of the newly started rsync process already anyway.
+	 */
+	.nice_local = 0,
+	.nice_remote = 0,
+
+	/* If set to other than 0, be ionice on the local or remote site
+	 * Currently only idle is supported for ionice when turned on.
+	 */
+	.ionice_local = 0,
+	.ionice_remote = 0,
+};
+
+/**
+ * Turn niceness off (no nice and no ionice)
+ */
+void niceness_turn_off()
+{
+	niceness.nice_local = 0;
+	niceness.nice_remote = 0;
+	niceness.ionice_local = 0;
+	niceness.ionice_remote = 0;
+}
+
+/**
+ * Turn niceness on (nice and ionice set to default values for maximum niceness)
+ */
+void niceness_turn_on()
+{
+	niceness.nice_local = NICENESS_RENICE_DEFAULT_PRIO;
+	niceness.nice_remote = NICENESS_RENICE_DEFAULT_PRIO;
+	niceness.ionice_local = NICENESS_IONICE_DEFAULT_PRIO;
+	niceness.ionice_remote = NICENESS_IONICE_DEFAULT_PRIO;
+}
+
+/**
+ * Apply nice/ionice local to this rsync process
+ */
+void niceness_renice_and_ionice_me()
+{
+	if (niceness.nice_local) {
+		niceness_renice_me(niceness.nice_local);
+	}
+
+	if (niceness.ionice_local) {
+		niceness_ionice_me(niceness.ionice_local);
+	}
+}

niceness/niceness.h

@@ -0,0 +1,128 @@
+/*
+ * Renice or ionice the rsync process to reduce its impact on the system
+ *
+ * Copyright (C) 2026 Michael Mess
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, visit the http://fsf.org website.
+ */
+
+#ifndef NICENESS_H // Ensure that this header file is never included more than once, thus avoiding errors with duplicate definitions
+#define NICENESS_H 1
+
+/*
+ * Enum for ionice values.
+ * Constants with negative numbers need root permission, others can be set by any user.
+ * RT_X is realtime priority
+ * BE_X is best effort with the given level
+ * IDLE means the process gets served only when no other processes are using disk io.
+ * NONE means best effort with level calculated by the formula (cpu_nice + 20) / 5
+ *      and is the default that does not need to be set.
+ */
+enum Ionice_Values {
+    RT_0 =-8,
+    RT_1 =-7,
+    RT_2 =-6,
+    RT_3 =-5,
+    RT_4 =-4,
+    RT_5 =-3,
+    RT_6 =-2,
+    RT_7 =-1,
+    NONE = 0,
+    BE_0 = 1,
+    BE_1 = 2,
+    BE_2 = 3,
+    BE_3 = 4,
+    BE_4 = 5,
+    BE_5 = 6,
+    BE_6 = 7,
+    BE_7 = 8,
+    IDLE = 9
+};
+
+/*
+ * String representation of ionice. All strings have to be 4 characters long.
+ */
+extern const char *Ionice_ValueStrings[];
+/*
+const char *Ionice_ValueStrings[] = {
+	"rt_0",
+	"rt_1",
+	"rt_2",
+	"rt_3",
+	"rt_4",
+	"rt_5",
+	"rt_6",
+	"rt_7",
+	"none",
+	"be_0",
+	"be_1",
+	"be_2",
+	"be_3",
+	"be_4",
+	"be_5",
+	"be_6",
+	"be_7",
+	"idle",
+	0
+};
+*/
+
+/*
+ * Constants to be used when no specific argument is given
+ */
+#define NICENESS_RENICE_DEFAULT_PRIO 19;
+#define NICENESS_IONICE_DEFAULT_PRIO IDLE;
+
+/*
+ * Struct to hold state for niceness
+ */
+struct niceness {
+	/* If set to other than 0, be nice on the local or remote site
+	* Contains the nice priority to be set on the process, or 0=feature is turned off, no priority will be set.
+	* I have to admit, that it is not possible to set a nice value of 0 with this code,
+	* but in most cases 0 should be the priority of the newly started rsync process already anyway.
+	*/
+	int nice_local;
+	int nice_remote;
+
+	/* If set to other than 0, be ionice on the local or remote site
+	* Currently only idle is supported for ionice when turned on.
+	*/
+	int ionice_local;
+	int ionice_remote;
+};
+
+extern struct niceness niceness;
+
+
+/*
+ * Some methods to simply turn niceness on or off or configure with an argument
+ */
+void niceness_turn_off();
+void niceness_turn_on();
+int niceness_parse_argument(const char * arg);
+
+/*
+ * Apply nice and ionice on this local process
+ */
+void niceness_renice_and_ionice_me();
+void niceness_renice_me(int prio);
+void niceness_ionice_me(int ionice_value);
+
+/*
+ * Utility function to get the string representation of an ionice value
+ */
+const char *intToIoniceValueString(int ionice_value);
+
+#endif // ifndef NICENESS_H