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Date: Mon, 24 Jan 2022 09:47:33 +0900
From: Dominique MARTINET <dominique.martinet@...ark-techno.com>
To: musl@...ts.openwall.com
Cc: Rich Felker <dalias@...c.org>, Ismael Luceno <ismael@...ev.co.uk>
Subject: Re: [PATCH v3 2/2] nftw: implement FTW_ACTIONRETVAL (GNU
extension)
This didn't get much traction when I submitted one last year:
https://www.openwall.com/lists/musl/2021/03/26/1
(and there were at least a couple other occurences I could find at the
time)
But given it keeps getting resubmitted I assume we can say that confirms
there's demand for it?
Ismael Luceno wrote on Sun, Jan 23, 2022 at 04:59:55PM +0100:
> diff --git a/include/ftw.h b/include/ftw.h
> index b15c062a8389..2e77dc76e11b 100644
> --- a/include/ftw.h
> +++ b/include/ftw.h
> @@ -21,6 +21,13 @@ extern "C" {
> #define FTW_CHDIR 4
> #define FTW_DEPTH 8
>
> +#define FTW_ACTIONRETVAL 16
> +/* return values for callback */
> +#define FTW_CONTINUE 0
> +#define FTW_STOP 1
> +#define FTW_SKIP_SUBTREE 2
> +#define FTW_SKIP_SIBLINGS 3
FWIW since this is a GNU extension I only had defined these in a
#ifdef _GNU_SOURCE block, but this had the ugly side effect of having to
redefine SUBTREE/SIBLINGS in the .c so I'm not sure which is better.
> +
> struct FTW {
> int base;
> int level;
> diff --git a/src/misc/nftw.c b/src/misc/nftw.c
> index 7569a657e54e..382169f66b8b 100644
> --- a/src/misc/nftw.c
> +++ b/src/misc/nftw.c
> @@ -26,7 +26,7 @@ static int do_nftw(char *path, int (*fn)(const char *, const struct stat *, int,
> struct stat st;
> struct history new;
> int type;
> - int r;
> + int r, r2;
> int dfd;
> int err;
> struct FTW lev;
> @@ -72,12 +72,19 @@ static int do_nftw(char *path, int (*fn)(const char *, const struct stat *, int,
> if (!fd_limit) close(dfd);
> }
>
> - if (!(flags & FTW_DEPTH) && (r=fn(path, &st, type, &lev)))
> - return r;
> + r = 0;
> + if (!(flags & FTW_DEPTH) && (r=fn(path, &st, type, &lev))) {
> + if ((flags & FTW_ACTIONRETVAL)) {
> + if (r == FTW_STOP) return FTW_STOP;
> + if (r == FTW_SKIP_SUBTREE) return 0;
> + /* other values are saved for when returning */
Hm, I'd naively think you would want to return immediately the other
values as well, so the else below is wrong?
But I didn't take long enough to check what e.g. a SKIP_SIBLINGS would
mean here, the construction just looks a bit odd to me.
> + } else
> + return r;
> + }
>
> for (; h; h = h->chain)
> if (h->dev == st.st_dev && h->ino == st.st_ino)
> - return 0;
> + return r;
>
> if ((type == FTW_D || type == FTW_DP) && fd_limit) {
> if (dfd < 0) {
> @@ -107,9 +114,12 @@ static int do_nftw(char *path, int (*fn)(const char *, const struct stat *, int,
> }
> path[j]='/';
> strcpy(path+j+1, de->d_name);
> - if ((r=do_nftw(path, fn, fd_limit-1, flags, &new))) {
> + if ((r2=do_nftw(path, fn, fd_limit-1, flags, &new))) {
> + if ((flags & FTW_ACTIONRETVAL)
> + && r2 == FTW_SKIP_SIBLINGS)
> + break;
> closedir(d);
> - return r;
> + return r2;
> }
> }
> closedir(d);
> @@ -120,10 +130,13 @@ static int do_nftw(char *path, int (*fn)(const char *, const struct stat *, int,
> }
>
> path[l] = 0;
> - if ((flags & FTW_DEPTH) && (r=fn(path, &st, type, &lev)))
> - return r;
> -
> - return 0;
> + if (flags & FTW_DEPTH) {
> + r = fn(path, &st, type, &lev);
> + /* ignore FTW_SKIP_SUBTREE (too late), the caller is broken */
> + if ((flags & FTW_ACTIONRETVAL) && r == FTW_SKIP_SUBTREE)
> + return 0;
IIRC the glibc implementation also ignores FTW_SKIP_SIBLINGS in that
case (nftw returns 0), I'm not sure how much of a 1-to-1 implementation
we want -- I had implemented my version through a black-box approach
with a client exercising all kind of different code paths as for a gnu
extension I'd assume glibc to be the reference.
I haven't taken the time to rerun that comparison (the test client is in
a comment in my patch), but I probably will if this looks like it would
get merged unless someone else did.
> + }
> + return r;
> }
>
> int nftw(const char *path, int (*fn)(const char *, const struct stat *, int, struct FTW *), int fd_limit, int flags)
--
Dominique
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