libc: Add inotify support

inotify_init() and inotify_init1() are implemented using __specialfd(2).
inotify_add_watch() is implemented in terms of inotify_add_watch_at(2).

Reviewed by:	kib
MFC after:	3 months
Sponsored by:	Klara, Inc.
Differential Revision:	https://reviews.freebsd.org/D50315

(cherry picked from commit 245ff4c4b2c2728674121a5d9736a5e079bd00b2)

4 files changed, 55 insertions, 0 deletions

diff --git a/lib/libc/gen/Makefile.inc b/lib/libc/gen/Makefile.inc
index 271340ca49f7..730be5f9a030 100644
--- a/lib/libc/gen/Makefile.inc
+++ b/lib/libc/gen/Makefile.inc
@@ -95,6 +95,7 @@ SRCS+=	__getosreldate.c \
 	glob.c \
 	glob-compat11.c \
 	initgroups.c \
+	inotify.c \
 	isatty.c \
 	isinf.c \
 	isnan.c \
diff --git a/lib/libc/gen/Symbol.map b/lib/libc/gen/Symbol.map
index 890d826c3c6e..7d27c9a79645 100644
--- a/lib/libc/gen/Symbol.map
+++ b/lib/libc/gen/Symbol.map
@@ -463,6 +463,9 @@ FBSD_1.8 {
 	execvpe;
 	fdscandir;
 	fdscandir_b;
+	inotify_add_watch;
+	inotify_init;
+	inotify_init1;
 	psiginfo;
 	rtld_get_var;
 	rtld_set_var;
diff --git a/lib/libc/gen/inotify.c b/lib/libc/gen/inotify.c
new file mode 100644
index 000000000000..b3590e0f5e4d
--- /dev/null
+++ b/lib/libc/gen/inotify.c
@@ -0,0 +1,49 @@
+/*-
+ * SPDX-License-Identifier: BSD-2-Clause
+ *
+ * Copyright (c) 2025 Klara, Inc.
+ */
+
+#include "namespace.h"
+#include <sys/types.h>
+#include <sys/fcntl.h>
+#include <sys/inotify.h>
+#include <sys/specialfd.h>
+#include "un-namespace.h"
+#include "libc_private.h"
+
+/*
+ * Provide compatibility with libinotify, which uses different values for these
+ * flags.
+ */
+#define	IN_NONBLOCK_OLD	0x80000
+#define	IN_CLOEXEC_OLD	0x00800
+
+int
+inotify_add_watch(int fd, const char *pathname, uint32_t mask)
+{
+	return (inotify_add_watch_at(fd, AT_FDCWD, pathname, mask));
+}
+
+int
+inotify_init1(int flags)
+{
+	struct specialfd_inotify args;
+
+	if ((flags & IN_NONBLOCK_OLD) != 0) {
+		flags &= ~IN_NONBLOCK_OLD;
+		flags |= IN_NONBLOCK;
+	}
+	if ((flags & IN_CLOEXEC_OLD) != 0) {
+		flags &= ~IN_CLOEXEC_OLD;
+		flags |= IN_CLOEXEC;
+	}
+	args.flags = flags;
+	return (__sys___specialfd(SPECIALFD_INOTIFY, &args, sizeof(args)));
+}
+
+int
+inotify_init(void)
+{
+	return (inotify_init1(0));
+}
diff --git a/lib/libc/sys/Symbol.map b/lib/libc/sys/Symbol.map
index 506d88d46c34..432e89c726e4 100644
--- a/lib/libc/sys/Symbol.map
+++ b/lib/libc/sys/Symbol.map
@@ -426,6 +426,8 @@ FBSD_1.7 {
 
 FBSD_1.8 {
 	getrlimitusage;
+	inotify_add_watch_at;
+	inotify_rm_watch;
 	kcmp;
 	setcred;
 };