static const char *
strcmp_prefix(const char *a, const char *a_prefix)
{
while (*a_prefix && *a == *a_prefix) {
a++;
a_prefix++;
}
return *a_prefix ? NULL : a;
}
/*
* In order to implement different sets of xattr operations for each xattr
* prefix with the generic xattr API, a filesystem should create a
* null-terminated array of struct xattr_handler (one for each prefix) and
* hang a pointer to it off of the s_xattr field of the superblock.
*
* The generic_fooxattr() functions will use this list to dispatch xattr
* operations to the correct xattr_handler.
*/
#define for_each_xattr_handler(handlers, handler) \
for ((handler) = *(handlers)++; \
(handler) != NULL; \
(handler) = *(handlers)++)
/*
* Find the xattr_handler with the matching prefix.
*/
static const struct xattr_handler *
xattr_resolve_name(const struct xattr_handler **handlers, const char **name)
{
const struct xattr_handler *handler;
if (!*name)
return NULL;
for_each_xattr_handler(handlers, handler) {
const char *n = strcmp_prefix(*name, handler->prefix);
if (n) {
*name = n;
break;
}
}
return handler;
}
/*
* Find the handler for the prefix and dispatch its get() operation.
*/
ssize_t
generic_getxattr(struct dentry *dentry, const char *name, void *buffer, size_t size)
{
const struct xattr_handler *handler;
handler = xattr_resolve_name(dentry->d_sb->s_xattr, &name);
if (!handler)
return -EOPNOTSUPP;
return handler->get(dentry, name, buffer, size, handler->flags);
}
/*
* Combine the results of the list() operation from every xattr_handler in the
* list.
*/
ssize_t
generic_listxattr(struct dentry *dentry, char *buffer, size_t buffer_size)
{
const struct xattr_handler *handler, **handlers = dentry->d_sb->s_xattr;
unsigned int size = 0;
if (!buffer) {
for_each_xattr_handler(handlers, handler) {
size += handler->list(dentry, NULL, 0, NULL, 0,
handler->flags);
}
} else {
char *buf = buffer;
for_each_xattr_handler(handlers, handler) {
size = handler->list(dentry, buf, buffer_size,
NULL, 0, handler->flags);
if (size > buffer_size)
return -ERANGE;
buf += size;
buffer_size -= size;
}
size = buf – buffer;
}
return size;
}
/*
* Find the handler for the prefix and dispatch its set() operation.
*/
int
generic_setxattr(struct dentry *dentry, const char *name, const void *value, size_t size, int flags)
{
const struct xattr_handler *handler;
if (size == 0)
value = “”; /* empty EA, do not remove */
handler = xattr_resolve_name(dentry->d_sb->s_xattr, &name);
if (!handler)
return -EOPNOTSUPP;
return handler->set(dentry, name, value, size, flags, handler->flags);
}
/*
* Find the handler for the prefix and dispatch its set() operation to remove
* any associated extended attribute.
*/
int
generic_removexattr(struct dentry *dentry, const char *name)
{
const struct xattr_handler *handler;
handler = xattr_resolve_name(dentry->d_sb->s_xattr, &name);
if (!handler)
return -EOPNOTSUPP;
return handler->set(dentry, name, NULL, 0,
XATTR_REPLACE, handler->flags);
}
EXPORT_SYMBOL(generic_getxattr);
EXPORT_SYMBOL(generic_listxattr);
EXPORT_SYMBOL(generic_setxattr);
EXPORT_SYMBOL(generic_removexattr);
