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Subject[PATCH v6 02/20] xattr: define vfs_getxattr_alloc and vfs_xattr_cmp
Date
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>
---
fs/xattr.c | 58 +++++++++++++++++++++++++++++++++++++++++++++++++
include/linux/xattr.h | 5 +++-
2 files changed, 62 insertions(+), 1 deletions(-)

diff --git a/fs/xattr.c b/fs/xattr.c
index f060663..851808c 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)
{
diff --git a/include/linux/xattr.h b/include/linux/xattr.h
index aed54c5..566b94b 100644
--- a/include/linux/xattr.h
+++ b/include/linux/xattr.h
@@ -78,7 +78,10 @@ ssize_t generic_getxattr(struct dentry *dentry, const char *name, void *buffer,
ssize_t generic_listxattr(struct dentry *dentry, char *buffer, size_t buffer_size);
int generic_setxattr(struct dentry *dentry, const char *name, const void *value, size_t size, int flags);
int generic_removexattr(struct dentry *dentry, const char *name);
-
+ssize_t vfs_getxattr_alloc(struct dentry *dentry, const char *name,
+ char **xattr_value, size_t size, gfp_t flags);
+int vfs_xattr_cmp(struct dentry *dentry, const char *xattr_name,
+ const char *value, size_t size, gfp_t flags);
#endif /* __KERNEL__ */

#endif /* _LINUX_XATTR_H */
--
1.7.3.4


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