Example code is provided.
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..c6ddb05 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 <attr/xattr.h>
+#include <sys/types.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
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