[PATCH v2 1/2] tools/nolibc: Add dirfd()

[Daniel Palmer <daniel@thingy.jp>]

This is useful for things like fstatat() on children of a directory
opened with opendir().

At the same time use the new internal helper to replace the two places
that are converting the DIR pointer back into an fd.

Signed-off-by: Daniel Palmer <daniel@thingy.jp>
---
 tools/include/nolibc/dirent.h | 38 +++++++++++++++++++++++++++--------
 1 file changed, 30 insertions(+), 8 deletions(-)

diff --git a/tools/include/nolibc/dirent.h b/tools/include/nolibc/dirent.h
index 4e02ef25e72d..d282ea8eb5d3 100644
--- a/tools/include/nolibc/dirent.h
+++ b/tools/include/nolibc/dirent.h
@@ -27,6 +27,18 @@ typedef struct {
 	char dummy[1];
 } DIR;
 
+/* Internal dirfd() that does not set errno */
+static __attribute__((unused))
+int __nolibc_dirfd(DIR *dirp)
+{
+	intptr_t i = (intptr_t)dirp;
+
+	if (i >= 0)
+		return -1;
+
+	return ~i;
+}
+
 static __attribute__((unused))
 DIR *fdopendir(int fd)
 {
@@ -49,15 +61,27 @@ DIR *opendir(const char *name)
 }
 
 static __attribute__((unused))
-int closedir(DIR *dirp)
+int dirfd(DIR *dirp)
 {
-	intptr_t i = (intptr_t)dirp;
+	int fd = __nolibc_dirfd(dirp);
 
-	if (i >= 0) {
+	if (fd < 0) {
 		SET_ERRNO(EBADF);
 		return -1;
 	}
-	return close(~i);
+
+	return fd;
+}
+
+static __attribute__((unused))
+int closedir(DIR *dirp)
+{
+	int fd = dirfd(dirp);
+
+	if (fd < 0)
+		return -1;
+
+	return close(fd);
 }
 
 static __attribute__((unused))
@@ -65,14 +89,12 @@ int readdir_r(DIR *dirp, struct dirent *entry, struct dirent **result)
 {
 	char buf[sizeof(struct linux_dirent64) + NAME_MAX + 1] __nolibc_aligned_as(struct linux_dirent64);
 	struct linux_dirent64 *ldir = (void *)buf;
-	intptr_t i = (intptr_t)dirp;
 	int fd, ret;
 
-	if (i >= 0)
+	fd = __nolibc_dirfd(dirp);
+	if (fd < 0)
 		return EBADF;
 
-	fd = ~i;
-
 	ret = _sys_getdents64(fd, ldir, sizeof(buf));
 	if (ret < 0)
 		return -ret;
-- 
2.53.0