xattr: define vfs_getxattr_alloc and vfs_xattr_cmp

vfs_getxattr_alloc() and vfs_xattr_cmp() are two new kernel xattr helper
functions.  vfs_getxattr_alloc() first allocates memory for the requested
xattr and then retrieves it. vfs_xattr_cmp() compares a given value with
the contents of an extended attribute.

Signed-off-by: Mimi Zohar <zohar@us.ibm.com>
Acked-by: Serge Hallyn <serge.hallyn@ubuntu.com>

1 files changed, 58 insertions, 0 deletions

diff --git a/fs/xattr.c b/fs/xattr.c
index f060663ab70c..851808c92b30 100644
--- a/fs/xattr.c
+++ b/fs/xattr.c
@@ -166,6 +166,64 @@ out_noalloc:
 }
 EXPORT_SYMBOL_GPL(xattr_getsecurity);
 
+/*
+ * vfs_getxattr_alloc - allocate memory, if necessary, before calling getxattr
+ *
+ * Allocate memory, if not already allocated, or re-allocate correct size,
+ * before retrieving the extended attribute.
+ *
+ * Returns the result of alloc, if failed, or the getxattr operation.
+ */
+ssize_t
+vfs_getxattr_alloc(struct dentry *dentry, const char *name, char **xattr_value,
+                   size_t xattr_size, gfp_t flags)
+{
+        struct inode *inode = dentry->d_inode;
+        char *value = *xattr_value;
+        int error;
+
+        error = xattr_permission(inode, name, MAY_READ);
+        if (error)
+                return error;
+
+        if (!inode->i_op->getxattr)
+                return -EOPNOTSUPP;
+
+        error = inode->i_op->getxattr(dentry, name, NULL, 0);
+        if (error < 0)
+                return error;
+
+        if (!value || (error > xattr_size)) {
+                value = krealloc(*xattr_value, error + 1, flags);
+                if (!value)
+                        return -ENOMEM;
+                memset(value, 0, error + 1);
+        }
+
+        error = inode->i_op->getxattr(dentry, name, value, error);
+        *xattr_value = value;
+        return error;
+}
+
+/* Compare an extended attribute value with the given value */
+int vfs_xattr_cmp(struct dentry *dentry, const char *xattr_name,
+                  const char *value, size_t size, gfp_t flags)
+{
+        char *xattr_value = NULL;
+        int rc;
+
+        rc = vfs_getxattr_alloc(dentry, xattr_name, &xattr_value, 0, flags);
+        if (rc < 0)
+                return rc;
+
+        if ((rc != size) || (memcmp(xattr_value, value, rc) != 0))
+                rc = -EINVAL;
+        else
+                rc = 0;
+        kfree(xattr_value);
+        return rc;
+}
+
 ssize_t
 vfs_getxattr(struct dentry *dentry, const char *name, void *value, size_t size)
 {