On Thu, Jan 30, 2025 at 08:54:03PM +0100, Thomas Weißschuh wrote:
From: Thomas Weißschuh thomas.weissschuh@linutronix.de
Add an allocation-free implementation of readdir() and related functions. The implementation is modelled after the one for FILE.
I think you'd need to mention/remind the two important points that come out of that choice, one being that DIR is a fake pointer that instead stores ~fd so that it can be turned back to a valid FD, and that subsequent readdir() calls will only work from the same file unit since it relies on a local static storage.
Better have this visible in the commit message so that in the event someone faces a difficulty due to this, they can easily find that it's an on-purpose design choice.
Signed-off-by: Thomas Weißschuh thomas.weissschuh@linutronix.de Signed-off-by: Thomas Weißschuh linux@weissschuh.net
I'm not entirely sure where to put it. It doesn't really belong into stdio.h, but that's where the FILE stuff is. sys.h wants alphabetical ordering, but IMO these functions should stick together.
My man pages suggest that userland code will include <dirent.h>, thus I think it could be the moment to create it with that new code.
diff --git a/tools/include/nolibc/stdio.h b/tools/include/nolibc/stdio.h index 3892034198dd566d21a5cc0a9f67cf097d428393..1f275a0a7b6b2c6f1c15405d027c282bb77aa618 100644 --- a/tools/include/nolibc/stdio.h +++ b/tools/include/nolibc/stdio.h
(...)
+static __attribute__((unused)) +struct dirent *readdir(DIR *dirp) +{
- static struct dirent dirent;
- char buf[sizeof(struct linux_dirent64) + NAME_MAX];
I'm uncertain where NAME_MAX is defined, I haven't found it in the nolibc sources, just double-checking that it's not just in your build environment by accident.
- struct linux_dirent64 *ldir = (void *)buf;
- intptr_t i = (intptr_t)dirp;
- int fd, ret;
- if (i >= 0) {
SET_ERRNO(EBADF);return NULL;- }
- fd = ~i;
- ret = getdents64(fd, ldir, sizeof(buf));
- if (ret == -1 || ret == 0)
return NULL;- /*
* getdents64() returns as many entries as fit the buffer.* readdir() can only return one entry at a time.* Make sure the non-returned ones are not skipped.*/- ret = lseek(fd, ldir->d_off, SEEK_SET);
- if (ret == -1)
return NULL;- dirent = (struct dirent) {
.d_ino = ldir->d_ino,- };
- strlcpy(dirent.d_name, ldir->d_name, sizeof(dirent.d_name));
Just out of curiosity, could this copy fail, and if so, should we handle it (e.g. NAME_MAX != 255) ? My guess here is that if it could almost never fail and checking it would needlessly complicate the function, let's just handle it with a comment for now. And if it cannot at all, let's mention why on top of it as well.
Thanks, Willy