[PATCH v5 4/8] vfs: plumb i_version handling into struct kstat

[Jeff Layton <jlayton@kernel.org>]

From: Jeff Layton <jlayton@redhat.com>

The NFS server has a lot of special handling for different types of
change attribute access, depending on what sort of inode we have. 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_INO_VERSION 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_INO_VERSION
off in requests from userland and in the result mask.

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

Signed-off-by: Jeff Layton <jlayton@kernel.org>
---
 fs/stat.c            | 14 +++++++++++++-
 include/linux/stat.h |  4 ++++
 2 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/fs/stat.c b/fs/stat.c
index 9ced8860e0f3..1a9c20ac5090 100644
--- a/fs/stat.c
+++ b/fs/stat.c
@@ -17,6 +17,7 @@
 #include <linux/syscalls.h>
 #include <linux/pagemap.h>
 #include <linux/compat.h>
+#include <linux/iversion.h>
 
 #include <linux/uaccess.h>
 #include <asm/unistd.h>
@@ -118,6 +119,11 @@ int vfs_getattr_nosec(const struct path *path, struct kstat *stat,
 	stat->attributes_mask |= (STATX_ATTR_AUTOMOUNT |
 				  STATX_ATTR_DAX);
 
+	if ((request_mask & STATX_INO_VERSION) && IS_I_VERSION(inode)) {
+		stat->result_mask |= STATX_INO_VERSION;
+		stat->ino_version = 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,
@@ -587,7 +593,8 @@ cp_statx(const struct kstat *stat, struct statx __user *buffer)
 
 	memset(&tmp, 0, sizeof(tmp));
 
-	tmp.stx_mask = stat->result_mask;
+	/* STATX_INO_VERSION is kernel-only for now */
+	tmp.stx_mask = stat->result_mask & ~STATX_INO_VERSION;
 	tmp.stx_blksize = stat->blksize;
 	tmp.stx_attributes = stat->attributes;
 	tmp.stx_nlink = stat->nlink;
@@ -626,6 +633,11 @@ int do_statx(int dfd, struct filename *filename, unsigned int flags,
 	if ((flags & AT_STATX_SYNC_TYPE) == AT_STATX_SYNC_TYPE)
 		return -EINVAL;
 
+	/* STATX_INO_VERSION is kernel-only for now. Ignore requests
+	 * from userland.
+	 */
+	mask &= ~STATX_INO_VERSION;
+
 	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 7df06931f25d..d482bbfc1358 100644
--- a/include/linux/stat.h
+++ b/include/linux/stat.h
@@ -50,6 +50,10 @@ struct kstat {
 	struct timespec64 btime;			/* File creation time */
 	u64		blocks;
 	u64		mnt_id;
+	u64		ino_version;
 };
 
+/* This definition is internal to the kernel for now. Mainly used by nfsd */
+#define STATX_INO_VERSION	0x40000000U	/* Want/got stx_change_attr */
+
 #endif
-- 
2.37.3