[PATCH v8 3/8] vfs: plumb i_version handling into struct kstat

Jeff Layton
2022-10-21T13:06:42Z

From: Jeff Layton <jlayton@redhat.com>

The NFS server has a lot of special handling for different types of
change attribute access, depending on the underlying filesystem. In
most cases, it's doing a getattr anyway and then fetching that value
after the fact.

Rather that do that, add a new STATX_CHANGE_COOKIE flag that is a
kernel-only symbol (for now). If requested and getattr can implement it,
it can fill out this field. For IS_I_VERSION inodes, add a generic
implementation in vfs_getattr_nosec. Take care to mask
STATX_CHANGE_COOKIE off in requests from userland and in the result
mask.

Since not all filesystems can give the same guarantees of monotonicity,
claim a STATX_ATTR_CHANGE_MONOTONIC flag that filesystems can set to
indicate that they offer an i_version value that can never go backward.

Eventually if we decide to make the i_version available to userland, we
can just designate a field for it in struct statx, and move the
STATX_CHANGE_COOKIE definition to the uapi header.

Reviewed-by: NeilBrown <neilb@suse.de>
Signed-off-by: Jeff Layton <jlayton@kernel.org>
---
fs/stat.c | 17 +++++++++++++++--
include/linux/stat.h | 9 +++++++++
2 files changed, 24 insertions(+), 2 deletions(-)

diff --git a/fs/stat.c b/fs/stat.c
index ef50573c72a2..06fd3fc1ab84 100644
--- a/fs/stat.c
+++ b/fs/stat.c
@@ -18,6 +18,7 @@
#include <linux/syscalls.h>
#include <linux/pagemap.h>
#include <linux/compat.h>
+#include <linux/iversion.h>

#include <linux/uaccess.h>
#include <asm/unistd.h>
@@ -119,6 +120,11 @@ int vfs_getattr_nosec(const struct path *path, struct kstat *stat,
stat->attributes_mask |= (STATX_ATTR_AUTOMOUNT |
STATX_ATTR_DAX);

+ if ((request_mask & STATX_CHANGE_COOKIE) && IS_I_VERSION(inode)) {
+ stat->result_mask |= STATX_CHANGE_COOKIE;
+ stat->change_cookie = inode_query_iversion(inode);
+ }
+
mnt_userns = mnt_user_ns(path->mnt);
if (inode->i_op->getattr)
return inode->i_op->getattr(mnt_userns, path, stat,
@@ -599,9 +605,11 @@ cp_statx(const struct kstat *stat, struct statx __user *buffer)

memset(&tmp, 0, sizeof(tmp));

- tmp.stx_mask = stat->result_mask;
+ /* STATX_CHANGE_COOKIE is kernel-only for now */
+ tmp.stx_mask = stat->result_mask & ~STATX_CHANGE_COOKIE;
tmp.stx_blksize = stat->blksize;
- tmp.stx_attributes = stat->attributes;
+ /* STATX_ATTR_CHANGE_MONOTONIC is kernel-only for now */
+ tmp.stx_attributes = stat->attributes & ~STATX_ATTR_CHANGE_MONOTONIC;
tmp.stx_nlink = stat->nlink;
tmp.stx_uid = from_kuid_munged(current_user_ns(), stat->uid);
tmp.stx_gid = from_kgid_munged(current_user_ns(), stat->gid);
@@ -640,6 +648,11 @@ int do_statx(int dfd, struct filename *filename, unsigned int flags,
if ((flags & AT_STATX_SYNC_TYPE) == AT_STATX_SYNC_TYPE)
return -EINVAL;

+ /* STATX_CHANGE_COOKIE is kernel-only for now. Ignore requests
+ * from userland.
+ */
+ mask &= ~STATX_CHANGE_COOKIE;
+
error = vfs_statx(dfd, filename, flags, &stat, mask);
if (error)
return error;
diff --git a/include/linux/stat.h b/include/linux/stat.h
index ff277ced50e9..52150570d37a 100644
--- a/include/linux/stat.h
+++ b/include/linux/stat.h
@@ -52,6 +52,15 @@ struct kstat {
u64 mnt_id;
u32 dio_mem_align;
u32 dio_offset_align;
+ u64 change_cookie;
};

+/* These definitions are internal to the kernel for now. Mainly used by nfsd. */
+
+/* mask values */
+#define STATX_CHANGE_COOKIE 0x40000000U /* Want/got stx_change_attr */
+
+/* file attribute values */
+#define STATX_ATTR_CHANGE_MONOTONIC 0x8000000000000000ULL /* version monotonically increases */
+
#endif
--
2.37.3