Revert "libc: Remove readdir_r(3)"

This reverts commit d549de7690.

ObsoleteFiles.inc

@@ -51,9 +51,6 @@
 #   xargs -n1 | sort | uniq -d;
 # done
 
-# 20250910: readdir_r(3) removed
-OLD_FILES+=usr/share/man/man3/readdir_r.3.gz
-
 # 20250826: Remove a misspelled manual
 OLD_FILES+=usr/share/man/man3/sysdecode_syscallnames.3.gz
 

include/dirent.h

@@ -115,6 +115,10 @@ DIR	*opendir(const char *);
 DIR	*fdopendir(int);
 struct dirent *
 	 readdir(DIR *);
+#if __POSIX_VISIBLE >= 199506 || __XSI_VISIBLE >= 500
+int	 readdir_r(DIR *, struct dirent *, struct dirent **)
+	__deprecated1("Does not take variable {NAME_MAX} into account");
+#endif
 void	 rewinddir(DIR *);
 #if __POSIX_VISIBLE >= 200809 || __XSI_VISIBLE >= 700
 int	 scandir(const char *, struct dirent ***,

lib/libc/gen/Makefile.inc

@@ -342,6 +342,7 @@ MLINKS+=directory.3 closedir.3 \
 	directory.3 fdopendir.3 \
 	directory.3 opendir.3 \
 	directory.3 readdir.3 \
+	directory.3 readdir_r.3 \
 	directory.3 rewinddir.3 \
 	directory.3 seekdir.3 \
 	directory.3 telldir.3

lib/libc/gen/Symbol.map

@@ -418,6 +418,7 @@ FBSD_1.5 {
 	globfree;
 	nftw;
 	readdir;
+	readdir_r;
 	scandir;
 	sem_clockwait_np;
 	setproctitle_fast;

lib/libc/gen/directory.3

@@ -25,13 +25,14 @@
 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 .\" SUCH DAMAGE.
 .\"
-.Dd September 5, 2025
+.Dd August 1, 2020
 .Dt DIRECTORY 3
 .Os
 .Sh NAME
 .Nm opendir ,
 .Nm fdopendir ,
 .Nm readdir ,
+.Nm readdir_r ,
 .Nm telldir ,
 .Nm seekdir ,
 .Nm rewinddir ,
@@ -49,6 +50,8 @@
 .Fn fdopendir "int fd"
 .Ft struct dirent *
 .Fn readdir "DIR *dirp"
+.Ft int
+.Fn readdir_r "DIR *dirp" "struct dirent *entry" "struct dirent **result"
 .Ft long
 .Fn telldir "DIR *dirp"
 .Ft void
@@ -62,6 +65,15 @@
 .Ft int
 .Fn dirfd "DIR *dirp"
 .Sh DESCRIPTION
+.Bf -symbolic
+The
+.Fn readdir_r
+interface is deprecated
+because it cannot be used correctly unless
+.Brq Va NAME_MAX
+is a fixed value.
+.Ef
+.Pp
 The
 .Fn opendir
 function
@@ -100,6 +112,7 @@ or to modify the state of the associated description other than by means
 of
 .Fn closedir ,
 .Fn readdir ,
+.Fn readdir_r ,
 or
 .Fn rewinddir ,
 the behavior is undefined.
@@ -131,6 +144,34 @@ may be set to any of the values documented for the
 system call.
 .Pp
 The
+.Fn readdir_r
+function
+provides the same functionality as
+.Fn readdir ,
+but the caller must provide a directory
+.Fa entry
+buffer to store the results in.
+The buffer must be large enough for a
+.Vt struct dirent
+with a
+.Va d_name
+array with
+.Brq Va NAME_MAX
++ 1 elements.
+If the read succeeds,
+.Fa result
+is pointed at the
+.Fa entry ;
+upon reaching the end of the directory
+.Fa result
+is set to
+.Dv NULL .
+The
+.Fn readdir_r
+function
+returns 0 on success or an error number to indicate failure.
+.Pp
+The
 .Fn telldir
 function
 returns a token representing the current location associated with the named
@@ -264,7 +305,9 @@ is not associated with a directory.
 .Pp
 The
 .Fn readdir
-function may also fail and set
+and
+.Fn readdir_r
+functions may also fail and set
 .Va errno
 for any of the errors specified for the routine
 .Xr getdents 2 .
@@ -295,6 +338,7 @@ The
 .Fn fdopendir ,
 .Fn opendir ,
 .Fn readdir ,
+.Fn readdir_r ,
 .Fn rewinddir ,
 .Fn seekdir
 and
@@ -347,8 +391,7 @@ will always set the correct location to return the same value as that last
 .Fn readdir
 performed.
 This is enough for some applications which want to
-.Dq push back the last entry read ,
-e.g. Samba.
+"push back the last entry read", e.g., Samba.
 Seeks back to any other location,
 other than the beginning of the directory,
 may result in unexpected behaviour if deletes are present.

lib/libc/gen/gen-compat.h

@@ -37,7 +37,6 @@ struct freebsd11_dirent;
 struct freebsd11_stat;
 struct freebsd11_statfs;
 
-int	freebsd15_readdir_r(DIR *, struct dirent *, struct dirent **);
 struct freebsd11_dirent *freebsd11_readdir(DIR *);
 int	freebsd11_readdir_r(DIR *, struct freebsd11_dirent *,
 	    struct freebsd11_dirent **);

lib/libc/gen/gen-private.h

@@ -60,4 +60,7 @@ struct _dirdesc {
 
 #define	_dirfd(dirp)	((dirp)->dd_fd)
 
+struct dirent;
+int __readdir_r(DIR *dirp, struct dirent *entry, struct dirent **result);
+
 #endif /* !_GEN_PRIVATE_H_ */

lib/libc/gen/readdir-compat11.c

@@ -95,7 +95,7 @@ freebsd11_readdir_r(DIR *dirp, struct freebsd11_dirent *entry,
 	struct dirent xentry, *xresult;
 	int error;
 
-	error = freebsd15_readdir_r(dirp, &xentry, &xresult);
+	error = __readdir_r(dirp, &xentry, &xresult);
 	if (error != 0)
 		return (error);
 	if (xresult != NULL) {

lib/libc/gen/readdir.c

@@ -41,8 +41,6 @@
 #include "gen-private.h"
 #include "telldir.h"
 
-#include "gen-compat.h"
-
 /*
  * get next entry in a directory.
  */
@@ -106,7 +104,7 @@ readdir(DIR *dirp)
 }
 
 int
-freebsd15_readdir_r(DIR *dirp, struct dirent *entry, struct dirent **result)
+__readdir_r(DIR *dirp, struct dirent *entry, struct dirent **result)
 {
 	struct dirent *dp;
 	int saved_errno;
@@ -135,4 +133,6 @@ freebsd15_readdir_r(DIR *dirp, struct dirent *entry, struct dirent **result)
 	return (0);
 }
 
-__sym_compat(readdir_r, freebsd15_readdir_r, FBSD_1.5);
+__strong_reference(__readdir_r, readdir_r);
+__warn_references(readdir_r,
+    "warning: this program uses readdir_r(), which is unsafe.");