[v4,01/19] fs: new API for handling inode->i_version
diff mbox

Message ID 20171222120556.7435-2-jlayton@kernel.org
State New
Headers show

Commit Message

Jeff Layton Dec. 22, 2017, 12:05 p.m. UTC
From: Jeff Layton <jlayton@redhat.com>

Add a documentation blob that explains what the i_version field is, how
it is expected to work, and how it is currently implemented by various
filesystems.

We already have inode_inc_iversion. Add several other functions for
manipulating and accessing the i_version counter. For now, the
implementation is trivial and basically works the way that all of the
open-coded i_version accesses work today.

Future patches will convert existing users of i_version to use the new
API, and then convert the backend implementation to do things more
efficiently.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
---
 fs/btrfs/file.c          |   1 +
 fs/btrfs/inode.c         |   1 +
 fs/btrfs/ioctl.c         |   1 +
 fs/btrfs/xattr.c         |   1 +
 fs/ext4/inode.c          |   1 +
 fs/ext4/namei.c          |   1 +
 fs/inode.c               |   1 +
 include/linux/fs.h       |  15 ----
 include/linux/iversion.h | 205 +++++++++++++++++++++++++++++++++++++++++++++++
 9 files changed, 212 insertions(+), 15 deletions(-)
 create mode 100644 include/linux/iversion.h

Comments

NeilBrown Dec. 22, 2017, 11:14 p.m. UTC | #1
On Fri, Dec 22 2017, Jeff Layton wrote:

> From: Jeff Layton <jlayton@redhat.com>
>
> Add a documentation blob that explains what the i_version field is, how
> it is expected to work, and how it is currently implemented by various
> filesystems.
>
> We already have inode_inc_iversion. Add several other functions for
> manipulating and accessing the i_version counter. For now, the
> implementation is trivial and basically works the way that all of the
> open-coded i_version accesses work today.
>
> Future patches will convert existing users of i_version to use the new
> API, and then convert the backend implementation to do things more
> efficiently.
>
> Signed-off-by: Jeff Layton <jlayton@redhat.com>
> ---
>  fs/btrfs/file.c          |   1 +
>  fs/btrfs/inode.c         |   1 +
>  fs/btrfs/ioctl.c         |   1 +
>  fs/btrfs/xattr.c         |   1 +
>  fs/ext4/inode.c          |   1 +
>  fs/ext4/namei.c          |   1 +
>  fs/inode.c               |   1 +
>  include/linux/fs.h       |  15 ----
>  include/linux/iversion.h | 205 +++++++++++++++++++++++++++++++++++++++++++++++
>  9 files changed, 212 insertions(+), 15 deletions(-)
>  create mode 100644 include/linux/iversion.h
>
> diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
> index eb1bac7c8553..c95d7b2efefb 100644
> --- a/fs/btrfs/file.c
> +++ b/fs/btrfs/file.c
> @@ -31,6 +31,7 @@
>  #include <linux/slab.h>
>  #include <linux/btrfs.h>
>  #include <linux/uio.h>
> +#include <linux/iversion.h>
>  #include "ctree.h"
>  #include "disk-io.h"
>  #include "transaction.h"
> diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
> index e1a7f3cb5be9..27f008b33fc1 100644
> --- a/fs/btrfs/inode.c
> +++ b/fs/btrfs/inode.c
> @@ -43,6 +43,7 @@
>  #include <linux/posix_acl_xattr.h>
>  #include <linux/uio.h>
>  #include <linux/magic.h>
> +#include <linux/iversion.h>
>  #include "ctree.h"
>  #include "disk-io.h"
>  #include "transaction.h"
> diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
> index 2ef8acaac688..aa452c9e2eff 100644
> --- a/fs/btrfs/ioctl.c
> +++ b/fs/btrfs/ioctl.c
> @@ -43,6 +43,7 @@
>  #include <linux/uuid.h>
>  #include <linux/btrfs.h>
>  #include <linux/uaccess.h>
> +#include <linux/iversion.h>
>  #include "ctree.h"
>  #include "disk-io.h"
>  #include "transaction.h"
> diff --git a/fs/btrfs/xattr.c b/fs/btrfs/xattr.c
> index 2c7e53f9ff1b..5258c1714830 100644
> --- a/fs/btrfs/xattr.c
> +++ b/fs/btrfs/xattr.c
> @@ -23,6 +23,7 @@
>  #include <linux/xattr.h>
>  #include <linux/security.h>
>  #include <linux/posix_acl_xattr.h>
> +#include <linux/iversion.h>
>  #include "ctree.h"
>  #include "btrfs_inode.h"
>  #include "transaction.h"
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index 7df2c5644e59..fa5d8bc52d2d 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -39,6 +39,7 @@
>  #include <linux/slab.h>
>  #include <linux/bitops.h>
>  #include <linux/iomap.h>
> +#include <linux/iversion.h>
>  
>  #include "ext4_jbd2.h"
>  #include "xattr.h"
> diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
> index 798b3ac680db..bcf0dff517be 100644
> --- a/fs/ext4/namei.c
> +++ b/fs/ext4/namei.c
> @@ -34,6 +34,7 @@
>  #include <linux/quotaops.h>
>  #include <linux/buffer_head.h>
>  #include <linux/bio.h>
> +#include <linux/iversion.h>
>  #include "ext4.h"
>  #include "ext4_jbd2.h"
>  
> diff --git a/fs/inode.c b/fs/inode.c
> index 03102d6ef044..19e72f500f71 100644
> --- a/fs/inode.c
> +++ b/fs/inode.c
> @@ -18,6 +18,7 @@
>  #include <linux/buffer_head.h> /* for inode_has_buffers */
>  #include <linux/ratelimit.h>
>  #include <linux/list_lru.h>
> +#include <linux/iversion.h>
>  #include <trace/events/writeback.h>
>  #include "internal.h"
>  
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 511fbaabf624..76382c24e9d0 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -2036,21 +2036,6 @@ static inline void inode_dec_link_count(struct inode *inode)
>  	mark_inode_dirty(inode);
>  }
>  
> -/**
> - * inode_inc_iversion - increments i_version
> - * @inode: inode that need to be updated
> - *
> - * Every time the inode is modified, the i_version field will be incremented.
> - * The filesystem has to be mounted with i_version flag
> - */
> -
> -static inline void inode_inc_iversion(struct inode *inode)
> -{
> -       spin_lock(&inode->i_lock);
> -       inode->i_version++;
> -       spin_unlock(&inode->i_lock);
> -}
> -
>  enum file_time_flags {
>  	S_ATIME = 1,
>  	S_MTIME = 2,
> diff --git a/include/linux/iversion.h b/include/linux/iversion.h
> new file mode 100644
> index 000000000000..bb50d27c71f9
> --- /dev/null
> +++ b/include/linux/iversion.h
> @@ -0,0 +1,205 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#ifndef _LINUX_IVERSION_H
> +#define _LINUX_IVERSION_H
> +
> +#include <linux/fs.h>
> +
> +/*
> + * The change attribute (i_version) is mandated by NFSv4 and is mostly for
> + * knfsd, but is also used for other purposes (e.g. IMA). The i_version must
> + * appear different to observers if there was a change to the inode's data or
> + * metadata since it was last queried.
> + *
> + * It should be considered an opaque value by observers. If it remains the same
                                 ^^^^^^^^^^^^

You keep using that word ... I don't think it means what you think it
means.
Change that sentence to:

    Observers see i_version as a 64 number which never decreases.

and the rest still makes perfect sense.

Thanks,
NeilBrown


> + * since it was last checked, then nothing has changed in the inode. If it's
> + * different then something has changed. Observers cannot infer anything about
> + * the nature or magnitude of the changes from the value, only that the inode
> + * has changed in some fashion.
> + *
> + * Not all filesystems properly implement the i_version counter. Subsystems that
> + * want to use i_version field on an inode should first check whether the
> + * filesystem sets the SB_I_VERSION flag (usually via the IS_I_VERSION macro).
> + *
> + * Those that set SB_I_VERSION will automatically have their i_version counter
> + * incremented on writes to normal files. If the SB_I_VERSION is not set, then
> + * the VFS will not touch it on writes, and the filesystem can use it how it
> + * wishes. Note that the filesystem is always responsible for updating the
> + * i_version on namespace changes in directories (mkdir, rmdir, unlink, etc.).
> + * We consider these sorts of filesystems to have a kernel-managed i_version.
> + *
> + * Note that some filesystems (e.g. NFS and AFS) just use the field to store
> + * a server-provided value (for the most part). For that reason, those
> + * filesystems do not set SB_I_VERSION. These filesystems are considered to
> + * have a self-managed i_version.
> + */
> +
> +/**
> + * inode_set_iversion_raw - set i_version to the specified raw value
> + * @inode: inode to set
> + * @new: new i_version value to set
> + *
> + * Set @inode's i_version field to @new. This function is for use by
> + * filesystems that self-manage the i_version.
> + *
> + * For example, the NFS client stores its NFSv4 change attribute in this way,
> + * and the AFS client stores the data_version from the server here.
> + */
> +static inline void
> +inode_set_iversion_raw(struct inode *inode, const u64 new)
> +{
> +	inode->i_version = new;
> +}
> +
> +/**
> + * inode_set_iversion - set i_version to a particular value
> + * @inode: inode to set
> + * @new: new i_version value to set
> + *
> + * Set @inode's i_version field to @new. This function is for filesystems with
> + * a kernel-managed i_version.
> + *
> + * For now, this just does the same thing as the _raw variant.
> + */
> +static inline void
> +inode_set_iversion(struct inode *inode, const u64 new)
> +{
> +	inode_set_iversion_raw(inode, new);
> +}
> +
> +/**
> + * inode_set_iversion_queried - set i_version to a particular value and set
> + *                              flag to indicate that it has been viewed
> + * @inode: inode to set
> + * @new: new i_version value to set
> + *
> + * When loading in an i_version value from a backing store, we typically don't
> + * know whether it was previously viewed before being stored or not. Thus, we
> + * must assume that it was, to ensure that any changes will result in the
> + * value changing.
> + *
> + * This function will set the inode's i_version, and possibly flag the value
> + * as if it has already been viewed at least once.
> + *
> + * For now, this just does what inode_set_iversion does.
> + */
> +static inline void
> +inode_set_iversion_queried(struct inode *inode, const u64 new)
> +{
> +	inode_set_iversion(inode, new);
> +}
> +
> +/**
> + * inode_maybe_inc_iversion - increments i_version
> + * @inode: inode with the i_version that should be updated
> + * @force: increment the counter even if it's not necessary
> + *
> + * Every time the inode is modified, the i_version field must be seen to have
> + * changed by any observer.
> + *
> + * In this implementation, we always increment it after taking the i_lock to
> + * ensure that we don't race with other incrementors.
> + *
> + * Returns true if counter was bumped, and false if it wasn't.
> + */
> +static inline bool
> +inode_maybe_inc_iversion(struct inode *inode, bool force)
> +{
> +	spin_lock(&inode->i_lock);
> +	inode->i_version++;
> +	spin_unlock(&inode->i_lock);
> +	return true;
> +}
> +
> +/**
> + * inode_inc_iversion - forcibly increment i_version
> + * @inode: inode that needs to be updated
> + *
> + * Forcbily increment the i_version field. This always results in a change to
> + * the observable value.
> + */
> +static inline void
> +inode_inc_iversion(struct inode *inode)
> +{
> +	inode_maybe_inc_iversion(inode, true);
> +}
> +
> +/**
> + * inode_iversion_need_inc - is the i_version in need of being incremented?
> + * @inode: inode to check
> + *
> + * Returns whether the inode->i_version counter needs incrementing on the next
> + * change.
> + *
> + * For now, we assume that it always does.
> + */
> +static inline bool
> +inode_iversion_need_inc(struct inode *inode)
> +{
> +	return true;
> +}
> +
> +/**
> + * inode_peek_iversion_raw - grab a "raw" iversion value
> + * @inode: inode from which i_version should be read
> + *
> + * Grab a "raw" inode->i_version value and return it. The i_version is not
> + * flagged or converted in any way. This is mostly used to access a self-managed
> + * i_version.
> + *
> + * With those filesystems, we want to treat the i_version as an entirely
> + * opaque value.
> + */
> +static inline u64
> +inode_peek_iversion_raw(const struct inode *inode)
> +{
> +	return inode->i_version;
> +}
> +
> +/**
> + * inode_peek_iversion - read i_version without flagging it to be incremented
> + * @inode: inode from which i_version should be read
> + *
> + * Read the inode i_version counter for an inode without registering it as a
> + * query.
> + *
> + * This is typically used by local filesystems that need to store an i_version
> + * on disk. In that situation, it's not necessary to flag it as having been
> + * viewed, as the result won't be used to gauge changes from that point.
> + */
> +static inline u64
> +inode_peek_iversion(const struct inode *inode)
> +{
> +	return inode_peek_iversion_raw(inode);
> +}
> +
> +/**
> + * inode_query_iversion - read i_version for later use
> + * @inode: inode from which i_version should be read
> + *
> + * Read the inode i_version counter. This should be used by callers that wish
> + * to store the returned i_version for later comparison. This will guarantee
> + * that a later query of the i_version will result in a different value if
> + * anything has changed.
> + *
> + * This implementation just does a peek.
> + */
> +static inline u64
> +inode_query_iversion(struct inode *inode)
> +{
> +	return inode_peek_iversion(inode);
> +}
> +
> +/**
> + * inode_cmp_iversion - check whether the i_version counter has changed
> + * @inode: inode to check
> + * @old: old value to check against its i_version
> + *
> + * Compare an i_version counter with a previous one. Returns 0 if they are
> + * the same or non-zero if they are different.
> + */
> +static inline s64
> +inode_cmp_iversion(const struct inode *inode, const u64 old)
> +{
> +	return (s64)inode_peek_iversion(inode) - (s64)old;
> +}
> +#endif
> -- 
> 2.14.3
>
> --
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Jeff Layton Dec. 22, 2017, 11:54 p.m. UTC | #2
On Sat, 2017-12-23 at 10:14 +1100, NeilBrown wrote:
> On Fri, Dec 22 2017, Jeff Layton wrote:
> 
> > From: Jeff Layton <jlayton@redhat.com>
> > 
> > Add a documentation blob that explains what the i_version field is, how
> > it is expected to work, and how it is currently implemented by various
> > filesystems.
> > 
> > We already have inode_inc_iversion. Add several other functions for
> > manipulating and accessing the i_version counter. For now, the
> > implementation is trivial and basically works the way that all of the
> > open-coded i_version accesses work today.
> > 
> > Future patches will convert existing users of i_version to use the new
> > API, and then convert the backend implementation to do things more
> > efficiently.
> > 
> > Signed-off-by: Jeff Layton <jlayton@redhat.com>
> > ---
> >  fs/btrfs/file.c          |   1 +
> >  fs/btrfs/inode.c         |   1 +
> >  fs/btrfs/ioctl.c         |   1 +
> >  fs/btrfs/xattr.c         |   1 +
> >  fs/ext4/inode.c          |   1 +
> >  fs/ext4/namei.c          |   1 +
> >  fs/inode.c               |   1 +
> >  include/linux/fs.h       |  15 ----
> >  include/linux/iversion.h | 205 +++++++++++++++++++++++++++++++++++++++++++++++
> >  9 files changed, 212 insertions(+), 15 deletions(-)
> >  create mode 100644 include/linux/iversion.h
> > 
> > diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
> > index eb1bac7c8553..c95d7b2efefb 100644
> > --- a/fs/btrfs/file.c
> > +++ b/fs/btrfs/file.c
> > @@ -31,6 +31,7 @@
> >  #include <linux/slab.h>
> >  #include <linux/btrfs.h>
> >  #include <linux/uio.h>
> > +#include <linux/iversion.h>
> >  #include "ctree.h"
> >  #include "disk-io.h"
> >  #include "transaction.h"
> > diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
> > index e1a7f3cb5be9..27f008b33fc1 100644
> > --- a/fs/btrfs/inode.c
> > +++ b/fs/btrfs/inode.c
> > @@ -43,6 +43,7 @@
> >  #include <linux/posix_acl_xattr.h>
> >  #include <linux/uio.h>
> >  #include <linux/magic.h>
> > +#include <linux/iversion.h>
> >  #include "ctree.h"
> >  #include "disk-io.h"
> >  #include "transaction.h"
> > diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
> > index 2ef8acaac688..aa452c9e2eff 100644
> > --- a/fs/btrfs/ioctl.c
> > +++ b/fs/btrfs/ioctl.c
> > @@ -43,6 +43,7 @@
> >  #include <linux/uuid.h>
> >  #include <linux/btrfs.h>
> >  #include <linux/uaccess.h>
> > +#include <linux/iversion.h>
> >  #include "ctree.h"
> >  #include "disk-io.h"
> >  #include "transaction.h"
> > diff --git a/fs/btrfs/xattr.c b/fs/btrfs/xattr.c
> > index 2c7e53f9ff1b..5258c1714830 100644
> > --- a/fs/btrfs/xattr.c
> > +++ b/fs/btrfs/xattr.c
> > @@ -23,6 +23,7 @@
> >  #include <linux/xattr.h>
> >  #include <linux/security.h>
> >  #include <linux/posix_acl_xattr.h>
> > +#include <linux/iversion.h>
> >  #include "ctree.h"
> >  #include "btrfs_inode.h"
> >  #include "transaction.h"
> > diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> > index 7df2c5644e59..fa5d8bc52d2d 100644
> > --- a/fs/ext4/inode.c
> > +++ b/fs/ext4/inode.c
> > @@ -39,6 +39,7 @@
> >  #include <linux/slab.h>
> >  #include <linux/bitops.h>
> >  #include <linux/iomap.h>
> > +#include <linux/iversion.h>
> >  
> >  #include "ext4_jbd2.h"
> >  #include "xattr.h"
> > diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
> > index 798b3ac680db..bcf0dff517be 100644
> > --- a/fs/ext4/namei.c
> > +++ b/fs/ext4/namei.c
> > @@ -34,6 +34,7 @@
> >  #include <linux/quotaops.h>
> >  #include <linux/buffer_head.h>
> >  #include <linux/bio.h>
> > +#include <linux/iversion.h>
> >  #include "ext4.h"
> >  #include "ext4_jbd2.h"
> >  
> > diff --git a/fs/inode.c b/fs/inode.c
> > index 03102d6ef044..19e72f500f71 100644
> > --- a/fs/inode.c
> > +++ b/fs/inode.c
> > @@ -18,6 +18,7 @@
> >  #include <linux/buffer_head.h> /* for inode_has_buffers */
> >  #include <linux/ratelimit.h>
> >  #include <linux/list_lru.h>
> > +#include <linux/iversion.h>
> >  #include <trace/events/writeback.h>
> >  #include "internal.h"
> >  
> > diff --git a/include/linux/fs.h b/include/linux/fs.h
> > index 511fbaabf624..76382c24e9d0 100644
> > --- a/include/linux/fs.h
> > +++ b/include/linux/fs.h
> > @@ -2036,21 +2036,6 @@ static inline void inode_dec_link_count(struct inode *inode)
> >  	mark_inode_dirty(inode);
> >  }
> >  
> > -/**
> > - * inode_inc_iversion - increments i_version
> > - * @inode: inode that need to be updated
> > - *
> > - * Every time the inode is modified, the i_version field will be incremented.
> > - * The filesystem has to be mounted with i_version flag
> > - */
> > -
> > -static inline void inode_inc_iversion(struct inode *inode)
> > -{
> > -       spin_lock(&inode->i_lock);
> > -       inode->i_version++;
> > -       spin_unlock(&inode->i_lock);
> > -}
> > -
> >  enum file_time_flags {
> >  	S_ATIME = 1,
> >  	S_MTIME = 2,
> > diff --git a/include/linux/iversion.h b/include/linux/iversion.h
> > new file mode 100644
> > index 000000000000..bb50d27c71f9
> > --- /dev/null
> > +++ b/include/linux/iversion.h
> > @@ -0,0 +1,205 @@
> > +/* SPDX-License-Identifier: GPL-2.0 */
> > +#ifndef _LINUX_IVERSION_H
> > +#define _LINUX_IVERSION_H
> > +
> > +#include <linux/fs.h>
> > +
> > +/*
> > + * The change attribute (i_version) is mandated by NFSv4 and is mostly for
> > + * knfsd, but is also used for other purposes (e.g. IMA). The i_version must
> > + * appear different to observers if there was a change to the inode's data or
> > + * metadata since it was last queried.
> > + *
> > + * It should be considered an opaque value by observers. If it remains the same
> 
>                                  ^^^^^^^^^^^^
> 
> You keep using that word ... I don't think it means what you think it
> means.
> Change that sentence to:
> 
>     Observers see i_version as a 64 number which never decreases.
> 
> and the rest still makes perfect sense.
> 

Thanks! Fixed in my tree. I'll not resend the set just for that though.

> > + * since it was last checked, then nothing has changed in the inode. If it's
> > + * different then something has changed. Observers cannot infer anything about
> > + * the nature or magnitude of the changes from the value, only that the inode
> > + * has changed in some fashion.
> > + *
> > + * Not all filesystems properly implement the i_version counter. Subsystems that
> > + * want to use i_version field on an inode should first check whether the
> > + * filesystem sets the SB_I_VERSION flag (usually via the IS_I_VERSION macro).
> > + *
> > + * Those that set SB_I_VERSION will automatically have their i_version counter
> > + * incremented on writes to normal files. If the SB_I_VERSION is not set, then
> > + * the VFS will not touch it on writes, and the filesystem can use it how it
> > + * wishes. Note that the filesystem is always responsible for updating the
> > + * i_version on namespace changes in directories (mkdir, rmdir, unlink, etc.).
> > + * We consider these sorts of filesystems to have a kernel-managed i_version.
> > + *
> > + * Note that some filesystems (e.g. NFS and AFS) just use the field to store
> > + * a server-provided value (for the most part). For that reason, those
> > + * filesystems do not set SB_I_VERSION. These filesystems are considered to
> > + * have a self-managed i_version.
> > + */
> > +
> > +/**
> > + * inode_set_iversion_raw - set i_version to the specified raw value
> > + * @inode: inode to set
> > + * @new: new i_version value to set
> > + *
> > + * Set @inode's i_version field to @new. This function is for use by
> > + * filesystems that self-manage the i_version.
> > + *
> > + * For example, the NFS client stores its NFSv4 change attribute in this way,
> > + * and the AFS client stores the data_version from the server here.
> > + */
> > +static inline void
> > +inode_set_iversion_raw(struct inode *inode, const u64 new)
> > +{
> > +	inode->i_version = new;
> > +}
> > +
> > +/**
> > + * inode_set_iversion - set i_version to a particular value
> > + * @inode: inode to set
> > + * @new: new i_version value to set
> > + *
> > + * Set @inode's i_version field to @new. This function is for filesystems with
> > + * a kernel-managed i_version.
> > + *
> > + * For now, this just does the same thing as the _raw variant.
> > + */
> > +static inline void
> > +inode_set_iversion(struct inode *inode, const u64 new)
> > +{
> > +	inode_set_iversion_raw(inode, new);
> > +}
> > +
> > +/**
> > + * inode_set_iversion_queried - set i_version to a particular value and set
> > + *                              flag to indicate that it has been viewed
> > + * @inode: inode to set
> > + * @new: new i_version value to set
> > + *
> > + * When loading in an i_version value from a backing store, we typically don't
> > + * know whether it was previously viewed before being stored or not. Thus, we
> > + * must assume that it was, to ensure that any changes will result in the
> > + * value changing.
> > + *
> > + * This function will set the inode's i_version, and possibly flag the value
> > + * as if it has already been viewed at least once.
> > + *
> > + * For now, this just does what inode_set_iversion does.
> > + */
> > +static inline void
> > +inode_set_iversion_queried(struct inode *inode, const u64 new)
> > +{
> > +	inode_set_iversion(inode, new);
> > +}
> > +
> > +/**
> > + * inode_maybe_inc_iversion - increments i_version
> > + * @inode: inode with the i_version that should be updated
> > + * @force: increment the counter even if it's not necessary
> > + *
> > + * Every time the inode is modified, the i_version field must be seen to have
> > + * changed by any observer.
> > + *
> > + * In this implementation, we always increment it after taking the i_lock to
> > + * ensure that we don't race with other incrementors.
> > + *
> > + * Returns true if counter was bumped, and false if it wasn't.
> > + */
> > +static inline bool
> > +inode_maybe_inc_iversion(struct inode *inode, bool force)
> > +{
> > +	spin_lock(&inode->i_lock);
> > +	inode->i_version++;
> > +	spin_unlock(&inode->i_lock);
> > +	return true;
> > +}
> > +
> > +/**
> > + * inode_inc_iversion - forcibly increment i_version
> > + * @inode: inode that needs to be updated
> > + *
> > + * Forcbily increment the i_version field. This always results in a change to
> > + * the observable value.
> > + */
> > +static inline void
> > +inode_inc_iversion(struct inode *inode)
> > +{
> > +	inode_maybe_inc_iversion(inode, true);
> > +}
> > +
> > +/**
> > + * inode_iversion_need_inc - is the i_version in need of being incremented?
> > + * @inode: inode to check
> > + *
> > + * Returns whether the inode->i_version counter needs incrementing on the next
> > + * change.
> > + *
> > + * For now, we assume that it always does.
> > + */
> > +static inline bool
> > +inode_iversion_need_inc(struct inode *inode)
> > +{
> > +	return true;
> > +}
> > +
> > +/**
> > + * inode_peek_iversion_raw - grab a "raw" iversion value
> > + * @inode: inode from which i_version should be read
> > + *
> > + * Grab a "raw" inode->i_version value and return it. The i_version is not
> > + * flagged or converted in any way. This is mostly used to access a self-managed
> > + * i_version.
> > + *
> > + * With those filesystems, we want to treat the i_version as an entirely
> > + * opaque value.
> > + */
> > +static inline u64
> > +inode_peek_iversion_raw(const struct inode *inode)
> > +{
> > +	return inode->i_version;
> > +}
> > +
> > +/**
> > + * inode_peek_iversion - read i_version without flagging it to be incremented
> > + * @inode: inode from which i_version should be read
> > + *
> > + * Read the inode i_version counter for an inode without registering it as a
> > + * query.
> > + *
> > + * This is typically used by local filesystems that need to store an i_version
> > + * on disk. In that situation, it's not necessary to flag it as having been
> > + * viewed, as the result won't be used to gauge changes from that point.
> > + */
> > +static inline u64
> > +inode_peek_iversion(const struct inode *inode)
> > +{
> > +	return inode_peek_iversion_raw(inode);
> > +}
> > +
> > +/**
> > + * inode_query_iversion - read i_version for later use
> > + * @inode: inode from which i_version should be read
> > + *
> > + * Read the inode i_version counter. This should be used by callers that wish
> > + * to store the returned i_version for later comparison. This will guarantee
> > + * that a later query of the i_version will result in a different value if
> > + * anything has changed.
> > + *
> > + * This implementation just does a peek.
> > + */
> > +static inline u64
> > +inode_query_iversion(struct inode *inode)
> > +{
> > +	return inode_peek_iversion(inode);
> > +}
> > +
> > +/**
> > + * inode_cmp_iversion - check whether the i_version counter has changed
> > + * @inode: inode to check
> > + * @old: old value to check against its i_version
> > + *
> > + * Compare an i_version counter with a previous one. Returns 0 if they are
> > + * the same or non-zero if they are different.
> > + */
> > +static inline s64
> > +inode_cmp_iversion(const struct inode *inode, const u64 old)
> > +{
> > +	return (s64)inode_peek_iversion(inode) - (s64)old;
> > +}
> > +#endif
> > -- 
> > 2.14.3
> > 
> > --
> > To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in
> > the body of a message to majordomo@vger.kernel.org
> > More majordomo info at  http://vger.kernel.org/majordomo-info.html
Jan Kara Jan. 2, 2018, 5:01 p.m. UTC | #3
On Fri 22-12-17 18:54:57, Jeff Layton wrote:
> On Sat, 2017-12-23 at 10:14 +1100, NeilBrown wrote:
> > > +#include <linux/fs.h>
> > > +
> > > +/*
> > > + * The change attribute (i_version) is mandated by NFSv4 and is mostly for
> > > + * knfsd, but is also used for other purposes (e.g. IMA). The i_version must
> > > + * appear different to observers if there was a change to the inode's data or
> > > + * metadata since it was last queried.
> > > + *
> > > + * It should be considered an opaque value by observers. If it remains the same
> > 
> >                                  ^^^^^^^^^^^^
> > 
> > You keep using that word ... I don't think it means what you think it
> > means.
> > Change that sentence to:
> > 
> >     Observers see i_version as a 64 number which never decreases.
> > 
> > and the rest still makes perfect sense.
> > 
> 
> Thanks! Fixed in my tree. I'll not resend the set just for that though.

With this fixed the patch looks good to me. You can add:

Reviewed-by: Jan Kara <jack@suse.cz>

								Honza

Patch
diff mbox

diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index eb1bac7c8553..c95d7b2efefb 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -31,6 +31,7 @@ 
 #include <linux/slab.h>
 #include <linux/btrfs.h>
 #include <linux/uio.h>
+#include <linux/iversion.h>
 #include "ctree.h"
 #include "disk-io.h"
 #include "transaction.h"
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index e1a7f3cb5be9..27f008b33fc1 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -43,6 +43,7 @@ 
 #include <linux/posix_acl_xattr.h>
 #include <linux/uio.h>
 #include <linux/magic.h>
+#include <linux/iversion.h>
 #include "ctree.h"
 #include "disk-io.h"
 #include "transaction.h"
diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 2ef8acaac688..aa452c9e2eff 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -43,6 +43,7 @@ 
 #include <linux/uuid.h>
 #include <linux/btrfs.h>
 #include <linux/uaccess.h>
+#include <linux/iversion.h>
 #include "ctree.h"
 #include "disk-io.h"
 #include "transaction.h"
diff --git a/fs/btrfs/xattr.c b/fs/btrfs/xattr.c
index 2c7e53f9ff1b..5258c1714830 100644
--- a/fs/btrfs/xattr.c
+++ b/fs/btrfs/xattr.c
@@ -23,6 +23,7 @@ 
 #include <linux/xattr.h>
 #include <linux/security.h>
 #include <linux/posix_acl_xattr.h>
+#include <linux/iversion.h>
 #include "ctree.h"
 #include "btrfs_inode.h"
 #include "transaction.h"
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 7df2c5644e59..fa5d8bc52d2d 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -39,6 +39,7 @@ 
 #include <linux/slab.h>
 #include <linux/bitops.h>
 #include <linux/iomap.h>
+#include <linux/iversion.h>
 
 #include "ext4_jbd2.h"
 #include "xattr.h"
diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
index 798b3ac680db..bcf0dff517be 100644
--- a/fs/ext4/namei.c
+++ b/fs/ext4/namei.c
@@ -34,6 +34,7 @@ 
 #include <linux/quotaops.h>
 #include <linux/buffer_head.h>
 #include <linux/bio.h>
+#include <linux/iversion.h>
 #include "ext4.h"
 #include "ext4_jbd2.h"
 
diff --git a/fs/inode.c b/fs/inode.c
index 03102d6ef044..19e72f500f71 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -18,6 +18,7 @@ 
 #include <linux/buffer_head.h> /* for inode_has_buffers */
 #include <linux/ratelimit.h>
 #include <linux/list_lru.h>
+#include <linux/iversion.h>
 #include <trace/events/writeback.h>
 #include "internal.h"
 
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 511fbaabf624..76382c24e9d0 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2036,21 +2036,6 @@  static inline void inode_dec_link_count(struct inode *inode)
 	mark_inode_dirty(inode);
 }
 
-/**
- * inode_inc_iversion - increments i_version
- * @inode: inode that need to be updated
- *
- * Every time the inode is modified, the i_version field will be incremented.
- * The filesystem has to be mounted with i_version flag
- */
-
-static inline void inode_inc_iversion(struct inode *inode)
-{
-       spin_lock(&inode->i_lock);
-       inode->i_version++;
-       spin_unlock(&inode->i_lock);
-}
-
 enum file_time_flags {
 	S_ATIME = 1,
 	S_MTIME = 2,
diff --git a/include/linux/iversion.h b/include/linux/iversion.h
new file mode 100644
index 000000000000..bb50d27c71f9
--- /dev/null
+++ b/include/linux/iversion.h
@@ -0,0 +1,205 @@ 
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _LINUX_IVERSION_H
+#define _LINUX_IVERSION_H
+
+#include <linux/fs.h>
+
+/*
+ * The change attribute (i_version) is mandated by NFSv4 and is mostly for
+ * knfsd, but is also used for other purposes (e.g. IMA). The i_version must
+ * appear different to observers if there was a change to the inode's data or
+ * metadata since it was last queried.
+ *
+ * It should be considered an opaque value by observers. If it remains the same
+ * since it was last checked, then nothing has changed in the inode. If it's
+ * different then something has changed. Observers cannot infer anything about
+ * the nature or magnitude of the changes from the value, only that the inode
+ * has changed in some fashion.
+ *
+ * Not all filesystems properly implement the i_version counter. Subsystems that
+ * want to use i_version field on an inode should first check whether the
+ * filesystem sets the SB_I_VERSION flag (usually via the IS_I_VERSION macro).
+ *
+ * Those that set SB_I_VERSION will automatically have their i_version counter
+ * incremented on writes to normal files. If the SB_I_VERSION is not set, then
+ * the VFS will not touch it on writes, and the filesystem can use it how it
+ * wishes. Note that the filesystem is always responsible for updating the
+ * i_version on namespace changes in directories (mkdir, rmdir, unlink, etc.).
+ * We consider these sorts of filesystems to have a kernel-managed i_version.
+ *
+ * Note that some filesystems (e.g. NFS and AFS) just use the field to store
+ * a server-provided value (for the most part). For that reason, those
+ * filesystems do not set SB_I_VERSION. These filesystems are considered to
+ * have a self-managed i_version.
+ */
+
+/**
+ * inode_set_iversion_raw - set i_version to the specified raw value
+ * @inode: inode to set
+ * @new: new i_version value to set
+ *
+ * Set @inode's i_version field to @new. This function is for use by
+ * filesystems that self-manage the i_version.
+ *
+ * For example, the NFS client stores its NFSv4 change attribute in this way,
+ * and the AFS client stores the data_version from the server here.
+ */
+static inline void
+inode_set_iversion_raw(struct inode *inode, const u64 new)
+{
+	inode->i_version = new;
+}
+
+/**
+ * inode_set_iversion - set i_version to a particular value
+ * @inode: inode to set
+ * @new: new i_version value to set
+ *
+ * Set @inode's i_version field to @new. This function is for filesystems with
+ * a kernel-managed i_version.
+ *
+ * For now, this just does the same thing as the _raw variant.
+ */
+static inline void
+inode_set_iversion(struct inode *inode, const u64 new)
+{
+	inode_set_iversion_raw(inode, new);
+}
+
+/**
+ * inode_set_iversion_queried - set i_version to a particular value and set
+ *                              flag to indicate that it has been viewed
+ * @inode: inode to set
+ * @new: new i_version value to set
+ *
+ * When loading in an i_version value from a backing store, we typically don't
+ * know whether it was previously viewed before being stored or not. Thus, we
+ * must assume that it was, to ensure that any changes will result in the
+ * value changing.
+ *
+ * This function will set the inode's i_version, and possibly flag the value
+ * as if it has already been viewed at least once.
+ *
+ * For now, this just does what inode_set_iversion does.
+ */
+static inline void
+inode_set_iversion_queried(struct inode *inode, const u64 new)
+{
+	inode_set_iversion(inode, new);
+}
+
+/**
+ * inode_maybe_inc_iversion - increments i_version
+ * @inode: inode with the i_version that should be updated
+ * @force: increment the counter even if it's not necessary
+ *
+ * Every time the inode is modified, the i_version field must be seen to have
+ * changed by any observer.
+ *
+ * In this implementation, we always increment it after taking the i_lock to
+ * ensure that we don't race with other incrementors.
+ *
+ * Returns true if counter was bumped, and false if it wasn't.
+ */
+static inline bool
+inode_maybe_inc_iversion(struct inode *inode, bool force)
+{
+	spin_lock(&inode->i_lock);
+	inode->i_version++;
+	spin_unlock(&inode->i_lock);
+	return true;
+}
+
+/**
+ * inode_inc_iversion - forcibly increment i_version
+ * @inode: inode that needs to be updated
+ *
+ * Forcbily increment the i_version field. This always results in a change to
+ * the observable value.
+ */
+static inline void
+inode_inc_iversion(struct inode *inode)
+{
+	inode_maybe_inc_iversion(inode, true);
+}
+
+/**
+ * inode_iversion_need_inc - is the i_version in need of being incremented?
+ * @inode: inode to check
+ *
+ * Returns whether the inode->i_version counter needs incrementing on the next
+ * change.
+ *
+ * For now, we assume that it always does.
+ */
+static inline bool
+inode_iversion_need_inc(struct inode *inode)
+{
+	return true;
+}
+
+/**
+ * inode_peek_iversion_raw - grab a "raw" iversion value
+ * @inode: inode from which i_version should be read
+ *
+ * Grab a "raw" inode->i_version value and return it. The i_version is not
+ * flagged or converted in any way. This is mostly used to access a self-managed
+ * i_version.
+ *
+ * With those filesystems, we want to treat the i_version as an entirely
+ * opaque value.
+ */
+static inline u64
+inode_peek_iversion_raw(const struct inode *inode)
+{
+	return inode->i_version;
+}
+
+/**
+ * inode_peek_iversion - read i_version without flagging it to be incremented
+ * @inode: inode from which i_version should be read
+ *
+ * Read the inode i_version counter for an inode without registering it as a
+ * query.
+ *
+ * This is typically used by local filesystems that need to store an i_version
+ * on disk. In that situation, it's not necessary to flag it as having been
+ * viewed, as the result won't be used to gauge changes from that point.
+ */
+static inline u64
+inode_peek_iversion(const struct inode *inode)
+{
+	return inode_peek_iversion_raw(inode);
+}
+
+/**
+ * inode_query_iversion - read i_version for later use
+ * @inode: inode from which i_version should be read
+ *
+ * Read the inode i_version counter. This should be used by callers that wish
+ * to store the returned i_version for later comparison. This will guarantee
+ * that a later query of the i_version will result in a different value if
+ * anything has changed.
+ *
+ * This implementation just does a peek.
+ */
+static inline u64
+inode_query_iversion(struct inode *inode)
+{
+	return inode_peek_iversion(inode);
+}
+
+/**
+ * inode_cmp_iversion - check whether the i_version counter has changed
+ * @inode: inode to check
+ * @old: old value to check against its i_version
+ *
+ * Compare an i_version counter with a previous one. Returns 0 if they are
+ * the same or non-zero if they are different.
+ */
+static inline s64
+inode_cmp_iversion(const struct inode *inode, const u64 old)
+{
+	return (s64)inode_peek_iversion(inode) - (s64)old;
+}
+#endif