JFS readdir() issues in stable 3.2

[Richard Weinberger <richard@nod.at>]

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Hi!

Mainline commit 44512449c0ab368889dd13ae0031fba74ee7e1d2
(jfs: fix readdir cookie incompatibility with NFSv4) does not work as expected on 3.2.
Maybe on other stable kernels too.

UML stumbled over it:
https://bugzilla.kernel.org/show_bug.cgi?id=94741

If you run the attached readdir.c on a JFS on stable 3.2.51+ readdir() will not
increment the directory offset nor return NULL, hence the caller will loop forever.
It looks like if the current directory offset is > 0 and you run seekdir(telldir())
the next readdir() call will not increment it.

Dave, has your fix some unnamed dependencies which need backporting too?

Thanks,
//richard

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#include <stdio.h>
#include <dirent.h>
#include <assert.h>

int main(int argc, char *argv[])
{
	DIR *dirp;
	struct dirent *dent;
	off_t dpos;

	if (argc < 2) {
		fprintf(stderr, "Usage: %s DIR\n", argv[0]);
		return 1;
	}

	dirp = opendir(argv[1]);
	assert(dirp);
	dpos = 0;

	for (;;) {
		seekdir(dirp, dpos);
		dent = readdir(dirp);
		if (!dent)
			break;
		assert(dpos != telldir(dirp));
		dpos = telldir(dirp);
	}

	return 0;
}