Use readdir on glibc >= 2.24 by default

readdir_r is deprecated as of glibc 2.24[1][2][3]

    The readdir_r() function was invented as a reentrant version of
    readdir(3).  It reads the next directory entry from the directory
    stream dirp, and returns it in the caller-allocated buffer pointed to
    by entry.  For details of the dirent structure, see readdir(3).

    A pointer to the returned buffer is placed in *result; if the end of
    the directory stream was encountered, then NULL is instead returned
    in *result.

    It is recommended that applications use readdir(3) instead of
    readdir_r().  Furthermore, since version 2.24, glibc deprecates
    readdir_r().  The reasons are as follows:

    *  On systems where NAME_MAX is undefined, calling readdir_r() may be
       unsafe because the interface does not allow the caller to specify
       the length of the buffer used for the returned directory entry.

    *  On some systems, readdir_r() can't read directory entries with
       very long names.  When the glibc implementation encounters such a
       name, readdir_r() fails with the error ENAMETOOLONG after the
       final directory entry has been read.  On some other systems,
       readdir_r() may return a success status, but the returned d_name
       field may not be null terminated or may be truncated.

    *  In the current POSIX.1 specification (POSIX.1-2008), readdir(3) is
       not required to be thread-safe.  However, in modern
       implementations (including the glibc implementation), concurrent
       calls to readdir(3) that specify different directory streams are
       thread-safe.  Therefore, the use of readdir_r() is generally
       unnecessary in multithreaded programs.  In cases where multiple
       threads must read from the same directory stream, using readdir(3)
       with external synchronization is still preferable to the use of
       readdir_r(), for the reasons given in the points above.

    *  It is expected that a future version of POSIX.1 will make
       readdir_r() obsolete, and require that readdir(3) be thread-safe
       when concurrently employed on different directory streams.

This patch introduces a new constant LUXIO_USE_READDIR,
luxio will use readdir instead of readdir_r iff this constant is defined.

LUXIO_USE_READDIR is automatically defined for glibc 2.24 or later.

[1]: http://man7.org/linux/man-pages/man3/readdir_r.3.html
[2]: https://lwn.net/Articles/696475/
[3]: https://sourceware.org/ml/libc-alpha/2016-02/msg00093.html

1 files changed, 29 insertions, 21 deletions

diff --git a/luxio.c b/luxio.c
index 4ba1a9b..739a055 100644
--- a/luxio.c
+++ b/luxio.c
@@ -61,6 +61,11 @@ Not all systems will provide all the functions described here.
 #include <syslog.h>
 #include <iconv.h>
 
+#if (__GLIBC__ == 2 && __GLIBC_MINOR__ >= 24)
+/* readdir is deprecated as of glibc 2.24, use readdir instead */
+#define LUXIO_USE_READDIR
+#endif
+
 #ifdef HAVE_SENDFILE
 # include <sys/sendfile.h>
 #endif
@@ -1077,34 +1082,37 @@ static int
 luxio_readdir(lua_State *L) /* 5.1.2 */
 {
 	luxio_readdir_state *s = luaL_checkudata(L, 1, LUXIO_READDIR_METATABLE);
-	int err;
 
-	err = readdir_r(s->dirp, s->buf, &s->ent);
-
-	if (err == 0 && s->ent != NULL) {
-		lua_pushinteger(L, 0);
-		lua_createtable(L, 0, 3);
-		lua_pushinteger(L, s->ent->d_ino);
-		lua_setfield(L, -2, "d_ino");
-		lua_pushstring(L, s->ent->d_name);
-		lua_setfield(L, -2, "d_name");
-#ifdef HAVE_D_TYPE
-		lua_pushinteger(L, s->ent->d_type);
-		lua_setfield(L, -2, "d_type");
+	errno = 0;
+#ifdef LUXIO_USE_READDIR
+	struct dirent *ent = readdir(s->dirp);
+#else
+	errno = readdir_r(s->dirp, s->buf, &s->ent);
+	struct dirent *ent = errno == 0 ? s->ent : NULL;
 #endif
-		return 2;
-	}
 
-	if (s->ent == NULL) {
-		/* end of directory */
-		lua_pushnil(L);
+	if (ent == NULL) {
+		if (errno != 0) {
+			lua_pushinteger(L, errno);
+		} else {
+			/* end of directory */
+			lua_pushnil(L);
+		}
 
 		return 1;
 	}
 
-	lua_pushinteger(L, err);
-
-	return 1;
+	lua_pushinteger(L, 0);
+	lua_createtable(L, 0, 3);
+	lua_pushinteger(L, ent->d_ino);
+	lua_setfield(L, -2, "d_ino");
+	lua_pushstring(L, ent->d_name);
+	lua_setfield(L, -2, "d_name");
+#ifdef HAVE_D_TYPE
+	lua_pushinteger(L, ent->d_type);
+	lua_setfield(L, -2, "d_type");
+#endif
+	return 2;
 }
 
 /*** Reset directory stream