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Errors from basic open_by_handle operations

To: xfs@xxxxxxxxxxx
Subject: Errors from basic open_by_handle operations
From: Mark Hills <mark.hills@xxxxxxxxxxxxxx>
Date: Thu, 9 Apr 2015 13:53:31 +0100 (BST)
Delivered-to: xfs@xxxxxxxxxxx
I am having troubles with elementary file handle functions in libhandle.

A basic open_by_handle is giving "Bad file descriptor".

But I am suspicious of a side effect; using path_to_fshandle earlier in 
the program changes these errors to "Operation not permitted".

Is there a basic mistake in my use of these calls, or a bug/unmaintained 
code?

I am on an XFS filesystem (otherwise the first call fails with 
'inappropriate ioctl'). The only documentation I can find is the man page; 
no mention about initialising the library, and I wasn't able to find any 
examples.

I'm on Scientific Linux 6.6 (like RedHat 6, kernel 2.6.32-504.1.3), and 
also tried updating to the latest xfsprogs from Git, with the same 
results.

Many thanks

-- 
Mark


$ ./test-xfs ~/scratch/tmp/xfs/file.c; echo $?
Handle 24 bytes: bd2c94ba959858e0000000870000000
readlink_by_handle: Bad file descriptor
open_by_handle: Bad file descriptor
0


$ ./test-xfs ~/scratch/tmp/xfs/file.c; echo $?
Handle 8 bytes: bd2c94ba959858
Handle 24 bytes: bd2c94ba959858e0000000870000000
readlink_by_handle: Operation not permitted
open_by_handle: Operation not permitted
0


/*
 * xfs file handle test
 *
 * compile with: gcc -o test-xfs test-xfs.c -lhandle -Wall
 */

#include <fcntl.h>
#include <limits.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <xfs/handle.h>

static void dump(FILE *f, void *m, size_t len)
{
        fprintf(f, "Handle %zu bytes: ", len);

        while (len--) {
                fprintf(f, "%hhx", *(unsigned char*)m);
                m++;
        }

        putchar('\n');
}

int main(int argc, char *argv[])
{
        int fd;
        char *pathname;
        void *hanp = NULL;
        size_t hlen;
        char buf[PATH_MAX];

        pathname = argv[1];

#if 0
        /*
         * Switching this section on changes changes the
         * errors from the later calls
         */

        if (path_to_fshandle(pathname, &hanp, &hlen) == -1) {
                perror("path_to_fshandle");
                return -1;
        }

        dump(stderr, hanp, hlen);

        free_handle(hanp, hlen);
#endif

        if (path_to_handle(pathname, &hanp, &hlen) == -1) {
                perror("path_to_handle");
                return -1;
        }

        dump(stderr, hanp, hlen);

        /*
         * The above calls were successful, but the next part always
         * fails
         */

        if (readlink_by_handle(hanp, hlen, buf, sizeof buf) == -1)
                perror("readlink_by_handle");
        else
                printf("Link: %s\n", buf);

        fd = open_by_handle(hanp, hlen, O_RDONLY);
        if (fd == -1) {
                perror("open_by_handle");
        } else {
                if (close(fd) == -1)
                        abort();
        }

        free_handle(hanp, hlen);

        return 0;
}

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