Hello Michael, listxattr is implemented individually by the different filesystems. Tmpfs delivered a double zero in my tests. The length included this double zero. I need to check the coding of all file systems. They might be different. Best regards Heinrich Schuchardt http://www.xypron.de Am 09.02.15 um 09:42 schrieb Michael Kerrisk (man-pages) > Hello Heinrich, > > > > On 02/08/2015 05:22 PM, Heinrich Schuchardt wrote: > > > The description of listxattr did not point out how that the array > > > of attributes itself is null-terminated. > > > > > > The missing information has been added. > > > > > > Furthermore example code is provided. > > > > Thanks for the patch. It is good to add an example program, but I think > > you have some details wrong. please see below. > > > > > Signed-off-by: Heinrich Schuchardt <xypron.glpk@xxxxxx> > > > --- > > > man2/listxattr.2 | 144 +++++++++++++++++++++++++++++++++++++++++++++++++++++-- > > > 1 file changed, 139 insertions(+), 5 deletions(-) > > > > > > diff --git a/man2/listxattr.2 b/man2/listxattr.2 > > > index a67592f..05197c4 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 > > > @@ -22,7 +23,7 @@ > > > .\" <http://www.gnu.org/licenses/>. > > > .\" %%%LICENSE_END > > > .\" > > > -.TH LISTXATTR 2 2014-02-06 "Linux" "Linux Programmer's Manual" > > > +.TH LISTXATTR 2 2015-02-08 "Linux" "Linux Programmer's Manual" > > > .SH NAME > > > listxattr, llistxattr, flistxattr \- list extended attribute names > > > .SH SYNOPSIS > > > @@ -95,13 +96,14 @@ size of a buffer which is sufficiently large to hold the list of names. > > > .SS Example > > > The > > > .I list > > > -of names is returned as an unordered array of null-terminated character > > > -strings (attribute names are separated by null bytes (\(aq\\0\(aq)), like this: > > > +of names is returned as a null-terminated unordered array of > > > +null-terminated character strings > > > +(attribute names are separated by null bytes (\(aq\\0\(aq)), like this: > > > .fam C > > > .RS > > > .nf > > > > > > -user.name1\\0system.name1\\0user.name2\\0 > > > +user.name1\\0system.name1\\0user.name2\\0\\0 > > > > I believe the above is incorrect. There is not, AFAIK, a double null byte > > at the end of the buffer. Rather, one determines the end of the list > > using the length returned by the listxattr(). Could you check this please. > > > > Thanks, > > > > Michael > > > > > > > .fi > > > .RE > > > .fam T > > > @@ -114,7 +116,7 @@ like this: > > > .RS > > > .nf > > > > > > -system.posix_acl_access\\0system.posix_acl_default\\0 > > > +system.posix_acl_access\\0system.posix_acl_default\\0\\0 > > > .fi > > > .RE > > > .fam T > > > @@ -150,6 +152,138 @@ 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. > > > + > > > +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 <attr/xattr.h> > > > +#include <sys/types.h> > > > + > > > +int > > > +main(int argc, char *argv[]) > > > +{ > > > + ssize_t buflen; > > > + char *buf, *p, *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 attribute list to the buffer > > > + */ > > > + buflen = listxattr(argv[1], buf, buflen); > > > + if (buflen == \-1) { > > > + perror("listxattr"); > > > + exit(EXIT_FAILURE); > > > + } > > > + > > > + /* > > > + * The end of the list is marked by zero terminated string > > > + * of length zero. > > > + */ > > > + p = buf; > > > + while (*p) { > > > + > > > + /* > > > + * output attribute name > > > + */ > > > + printf("%s: ", p); > > > + > > > + /* > > > + * determine length of value > > > + */ > > > + buflen = getxattr(argv[1], p, NULL, 0); > > > + if (buflen == \-1) > > > + perror("getxattr"); > > > + > > > + if (buflen > 0) { > > > + /* > > > + * allocate value buffer > > > + */ > > > + val = malloc(buflen); > > > + if (val == NULL) { > > > + perror("malloc"); > > > + exit(EXIT_FAILURE); > > > + } > > > + > > > + /* > > > + * read value to buffer > > > + */ > > > + buflen = getxattr(argv[1], p, val, buflen); > > > + if (buflen == \-1) > > > + perror("getxattr"); > > > + else > > > + /* > > > + * output attribute value > > > + */ > > > + printf("%s", val); > > > + > > > + free(val); > > > + } else > > > + printf("<no value>"); > > > + > > > + printf("\\n"); > > > + > > > + /* > > > + *forward to next attribute name > > > + */ > > > + while(*++p); > > > + ++p; > > > + } > > > + > > > + free(buf); > > > + exit(EXIT_SUCCESS); > > > +} > > > +.nf > > > +.fi > > > .SH SEE ALSO > > > .BR getfattr (1), > > > .BR setfattr (1), > > > > > > > > > -- > > Michael Kerrisk > > Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ > > Linux/UNIX System Programming Training: http://man7.org/training/ -- To unsubscribe from this list: send the line "unsubscribe linux-man" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
