Commit a1175d6b authored by Jeff Layton's avatar Jeff Layton
Browse files

vfs: plumb i_version handling into struct kstat 



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: default avatarNeilBrown <neilb@suse.de>
Reviewed-by: default avatarJan Kara <jack@suse.cz>
Signed-off-by: default avatarJeff Layton <jlayton@kernel.org>
parent a3bb7103

fs/stat.c

+15 −2
Original line number Diff line number Diff line
@@ -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>
@@ -122,6 +123,11 @@ 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,
@@ -602,9 +608,11 @@ 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);
@@ -643,6 +651,11 @@ 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;

include/linux/stat.h

+9 −0
Original line number Diff line number Diff line
@@ -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