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These allow extra metadata to be attached to files.

I think the functions should:
- accept both str and bytes for keys and values; when it's an str, encoding it using the FS encoding
- return str for attribute names, using the FS encoding
- return bytes for attribute values, although returning str might be reasonable as well
I also get the following test failures:
======================================================================
FAIL: test_fds (test.test_os.ExtendedAttributeTests)
----------------------------------------------------------------------
Traceback (most recent call last):
 File "/home/antoine/cpython/default/Lib/test/test_os.py", line 1579, in test_fds
 self._check_xattrs(getxattr, setxattr, removexattr, listxattr)
 File "/home/antoine/cpython/default/Lib/test/test_os.py", line 1542, in _check_xattrs
 setxattr(fn, b"user.test", b"bye", os.XATTR_CREATE)
AssertionError: OSError not raised
======================================================================
FAIL: test_lpath (test.test_os.ExtendedAttributeTests)
----------------------------------------------------------------------
Traceback (most recent call last):
 File "/home/antoine/cpython/default/Lib/test/test_os.py", line 1564, in test_lpath
 os.llistxattr)
 File "/home/antoine/cpython/default/Lib/test/test_os.py", line 1542, in _check_xattrs
 setxattr(fn, b"user.test", b"bye", os.XATTR_CREATE)
AssertionError: OSError not raised
======================================================================
FAIL: test_simple (test.test_os.ExtendedAttributeTests)
----------------------------------------------------------------------
Traceback (most recent call last):
 File "/home/antoine/cpython/default/Lib/test/test_os.py", line 1560, in test_simple
 os.listxattr)
 File "/home/antoine/cpython/default/Lib/test/test_os.py", line 1542, in _check_xattrs
 setxattr(fn, b"user.test", b"bye", os.XATTR_CREATE)
AssertionError: OSError not raised

Here is a new patch, implementing Antoine's suggestions.

And here is the next version, taking into account neologix's review.

Is it normal that listxattr() succeeds but getxattr() fails with ENOTSUPP?
>>> os.listxattr("/")
[]
>>> os.getxattr("/", "foo")
Traceback (most recent call last):
 File "<stdin>", line 1, in <module>
OSError: [Errno 95] Operation not supported
This is on 2.6.38.8.

2011年8月28日 Antoine Pitrou <report@bugs.python.org>:
>
> Antoine Pitrou <pitrou@free.fr> added the comment:
>
> Is it normal that listxattr() succeeds but getxattr() fails with ENOTSUPP?
>
>>>> os.listxattr("/")
> []
>>>> os.getxattr("/", "foo")
> Traceback (most recent call last):
> File "<stdin>", line 1, in <module>
> OSError: [Errno 95] Operation not supported
The reason you're getting ENOSUP is you have to use the proper prefix.
"user.*" for example.

After Antoine's review...

New changeset 4eb0b1819bda by Benjamin Peterson in branch 'default':
expose linux extended file system attributes (closes #12720)
http://hg.python.org/cpython/rev/4eb0b1819bda 

There is an inconsistency in used header and library.
attr/xattr.h and libattr.so belong to attr package (http://savannah.nongnu.org/projects/attr).
glibc provides sys/xattr.h and libc.so.
Both libattr.so and libc.so define getxattr(), setxattr() and other functions.
Modules/posixmodule.c includes attr/xattr.h from attr package, but libpython3.3.so isn't linked against libattr.so and is linked against libc.so, so functions from glibc are used at run time.
I suggest to use sys/xattr.h:
- sys/xattr.h instead of attr/xattr.h in Modules/posixmodule.c, configure, configure.in and pyconfig.h.in
- HAVE_SYS_XATTR_H instead of HAVE_ATTR_XATTR_H in Modules/posixmodule.c and pyconfig.h.in

New changeset 33f7044b5682 by Benjamin Peterson in branch 'default':
Use xattr functions from sys/xattr.h instead of attr/xattr.h (closes #12720)
http://hg.python.org/cpython/rev/33f7044b5682 

The OS X buildbots fail to compile posixmodule.c:
gcc -fno-strict-aliasing -g -O0 -Wall -Wstrict-prototypes -I. -I./Include -DPy_BUILD_CORE -c ./Modules/posixmodule.c -o Modules/posixmodule.o
./Modules/posixmodule.c: In function ‘try_getxattr’:
./Modules/posixmodule.c:10045: error: ‘XATTR_SIZE_MAX’ undeclared (first use in this function)
./Modules/posixmodule.c:10045: error: (Each undeclared identifier is reported only once
./Modules/posixmodule.c:10045: error: for each function it appears in.)
./Modules/posixmodule.c: In function ‘getxattr_common’:
./Modules/posixmodule.c:10083: error: ‘XATTR_SIZE_MAX’ undeclared (first use in this function)
./Modules/posixmodule.c: In function ‘posix_getxattr’:
./Modules/posixmodule.c:10101: warning: passing argument 3 of ‘getxattr_common’ from incompatible pointer type
./Modules/posixmodule.c: In function ‘posix_lgetxattr’:
./Modules/posixmodule.c:10119: error: ‘lgetxattr’ undeclared (first use in this function)
./Modules/posixmodule.c: In function ‘wrap_fgetxattr’:
./Modules/posixmodule.c:10129: error: too few arguments to function ‘fgetxattr’
./Modules/posixmodule.c:10130: warning: control reaches end of non-void function
./Modules/posixmodule.c: In function ‘posix_setxattr’:
./Modules/posixmodule.c:10165: error: too few arguments to function ‘setxattr’
./Modules/posixmodule.c: In function ‘posix_lsetxattr’:
./Modules/posixmodule.c:10190: warning: implicit declaration of function ‘lsetxattr’
./Modules/posixmodule.c: In function ‘posix_fsetxattr’:
./Modules/posixmodule.c:10216: error: too few arguments to function ‘fsetxattr’
./Modules/posixmodule.c: In function ‘posix_removexattr’:
./Modules/posixmodule.c:10239: error: too few arguments to function ‘removexattr’
./Modules/posixmodule.c: In function ‘posix_lremovexattr’:
./Modules/posixmodule.c:10262: warning: implicit declaration of function ‘lremovexattr’
./Modules/posixmodule.c: In function ‘posix_fremovexattr’:
./Modules/posixmodule.c:10285: error: too few arguments to function ‘fremovexattr’
./Modules/posixmodule.c: In function ‘listxattr_common’:
./Modules/posixmodule.c:10327: error: ‘XATTR_LIST_MAX’ undeclared (first use in this function)
./Modules/posixmodule.c: In function ‘posix_listxattr’:
./Modules/posixmodule.c:10369: warning: passing argument 2 of ‘listxattr_common’ from incompatible pointer type
./Modules/posixmodule.c: In function ‘posix_llistxattr’:
./Modules/posixmodule.c:10385: error: ‘llistxattr’ undeclared (first use in this function)
./Modules/posixmodule.c: In function ‘wrap_flistxattr’:
./Modules/posixmodule.c:10394: error: too few arguments to function ‘flistxattr’
./Modules/posixmodule.c:10395: warning: control reaches end of non-void function
./Modules/posixmodule.c: In function ‘all_ins’:
./Modules/posixmodule.c:11342: error: ‘XATTR_SIZE_MAX’ undeclared (first use in this function)
make: *** [Modules/posixmodule.o] Error 1
program finished with exit code 2
elapsedTime=20.601350

New changeset f325439d7f84 by Benjamin Peterson in branch 'default':
only compile xattrs on glibc (closes #12720)
http://hg.python.org/cpython/rev/f325439d7f84