Hello Heinrich,
On 10 February 2015 at 22:06, Heinrich Schuchardt <xypron.glpk@xxxxxx> wrote:
> Example code is provided.
>
> Version 4:
> Use #include <sys/xattr.h>
Thanks. Applied.
Cheers,
Michael
> Version 3:
> Remove unused variable.
> Use strlen instead of while(++p) to find end of string.
> Rename some variables.
> Correct comments.
>
> Version 2:
>
> As Michael correctly pointed out, the buffer length returned by
> listxattr does not contain any byte after the 0x00 indicating
> the end of the last list entry.
>
> Signed-off-by: Heinrich Schuchardt <xypron.glpk@xxxxxx>
> ---
> man2/listxattr.2 | 142 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 142 insertions(+)
>
> diff --git a/man2/listxattr.2 b/man2/listxattr.2
> index a67592f..5fd9ec7 100644
> --- a/man2/listxattr.2
> +++ b/man2/listxattr.2
> @@ -1,5 +1,6 @@
> .\" Copyright (C) Andreas Gruenbacher, February 2001
> .\" Copyright (C) Silicon Graphics Inc, September 2001
> +.\" Copyright (C) 2015 Heinrich Schuchardt <xypron.glpk@xxxxxx>
> .\"
> .\" %%%LICENSE_START(GPLv2+_DOC_FULL)
> .\" This is free documentation; you can redistribute it and/or
> @@ -150,6 +151,147 @@ These system calls are Linux-specific.
> .\" and the SGI XFS development team,
> .\" .RI < linux-xfs@xxxxxxxxxxx >.
> .\" Please send any bug reports or comments to these addresses.
> +.SH EXAMPLE
> +The following program demonstrates the usage of
> +.BR listxattr ()
> +and
> +.BR getxattr (2).
> +For a path provided, it lists all extended file attributes and their values.
> +
> +To keep the code simple, the assumption is made that attribute keys and
> +values are constant during the runtime of the program.
> +A production program should expect and handle changes during the runtime.
> +
> +The following output was recorded when first creating a file, setting
> +some extended file attributes, and then listing them with the example code.
> +
> +.SS Example output
> +.in +4n
> +.nf
> +$ touch /tmp/foo
> +$ setfattr -n user.fred -v chocolate /tmp/foo
> +$ setfattr -n user.frieda -v bar /tmp/foo
> +$ setfattr -n user.empty /tmp/foo
> +$ ./listxattr /tmp/foo
> +user.fred: chocolate
> +user.frieda: bar
> +user.empty: <no value>
> +.fi
> +.in
> +.SS Program source
> +.nf
> +#include <malloc.h>
> +#include <stdio.h>
> +#include <stdlib.h>
> +#include <string.h>
> +#include <sys/types.h>
> +#include <sys/xattr.h>
> +
> +int
> +main(int argc, char *argv[])
> +{
> + ssize_t buflen, keylen, vallen;
> + char *buf, *key, *val;
> +
> + if (argc != 2) {
> + fprintf(stderr, "Usage: %s path\\n", argv[0]);
> + exit(EXIT_FAILURE);
> + }
> +
> + /*
> + * Determine the length of the buffer needed.
> + */
> + buflen = listxattr(argv[1], NULL, 0);
> + if (buflen == \-1) {
> + perror("listxattr");
> + exit(EXIT_FAILURE);
> + }
> + if (buflen == 0) {
> + printf("%s has no attibutes.\\n", argv[1]);
> + exit(EXIT_SUCCESS);
> + }
> +
> + /*
> + * Allocate the buffer.
> + */
> + buf = malloc(buflen);
> + if (buf == NULL) {
> + perror("malloc");
> + exit(EXIT_FAILURE);
> + }
> +
> + /*
> + * Copy the list of attribute keys to the buffer.
> + */
> + buflen = listxattr(argv[1], buf, buflen);
> + if (buflen == \-1) {
> + perror("listxattr");
> + exit(EXIT_FAILURE);
> + }
> +
> + /*
> + * Loop over the list of zero terminated strings with the attribute keys.
> + * Use the remaining buffer length to determine the end of the list.
> + */
> + key = buf;
> + while (buflen > 0) {
> +
> + /*
> + * Output attribute key.
> + */
> + printf("%s: ", key);
> +
> + /*
> + * Determine length of the value.
> + */
> + vallen = getxattr(argv[1], key, NULL, 0);
> + if (vallen == \-1)
> + perror("getxattr");
> +
> + if (vallen > 0) {
> +
> + /*
> + * Allocate value buffer.
> + * One extra byte is needed to append 0x00.
> + */
> + val = malloc(vallen + 1);
> + if (val == NULL) {
> + perror("malloc");
> + exit(EXIT_FAILURE);
> + }
> +
> + /*
> + * Copy value to buffer.
> + */
> + vallen = getxattr(argv[1], key, val, vallen);
> + if (vallen == \-1)
> + perror("getxattr");
> + else {
> + /*
> + * Output attribute value.
> + */
> + val[vallen] = 0;
> + printf("%s", val);
> + }
> +
> + free(val);
> + } else if (vallen == 0)
> + printf("<no value>");
> +
> + printf("\\n");
> +
> + /*
> + * Forward to next attribute key.
> + */
> + keylen = strlen(key) + 1;
> + buflen \-= keylen;
> + key += keylen;
> + }
> +
> + free(buf);
> + exit(EXIT_SUCCESS);
> +}
> +.fi
> .SH SEE ALSO
> .BR getfattr (1),
> .BR setfattr (1),
> --
> 2.1.4
>
--
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/
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