From: NeilBrown Subject: Re: [PATCH v4 01/19] fs: new API for handling inode->i_version Date: Sat, 23 Dec 2017 10:14:18 +1100 Message-ID: <87zi6a73ud.fsf@notabene.neil.brown.name> References: <20171222120556.7435-1-jlayton@kernel.org> <20171222120556.7435-2-jlayton@kernel.org> Mime-Version: 1.0 Content-Type: multipart/signed; boundary="=-=-="; micalg=pgp-sha256; protocol="application/pgp-signature" Cc: linux-kernel@vger.kernel.org, viro@zeniv.linux.org.uk, linux-nfs@vger.kernel.org, bfields@fieldses.org, neilb@suse.de, jack@suse.de, linux-ext4@vger.kernel.org, tytso@mit.edu, adilger.kernel@dilger.ca, linux-xfs@vger.kernel.org, darrick.wong@oracle.com, david@fromorbit.com, linux-btrfs@vger.kernel.org, clm@fb.com, jbacik@fb.com, dsterba@suse.com, linux-integrity@vger.kernel.org, zohar@linux.vnet.ibm.com, dmitry.kasatkin@gmail.com, linux-afs@lists.infradead.org, dhowells@redhat.com, jaltman@auristor.com To: Jeff Layton , linux-fsdevel@vger.kernel.org Return-path: In-Reply-To: <20171222120556.7435-2-jlayton@kernel.org> Sender: linux-btrfs-owner@vger.kernel.org List-Id: linux-ext4.vger.kernel.org --=-=-= Content-Type: text/plain Content-Transfer-Encoding: quoted-printable On Fri, Dec 22 2017, Jeff Layton wrote: > From: Jeff Layton > > 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 > --- > 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 > #include > #include > +#include > #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 > #include > #include > +#include > #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 > #include > #include > +#include > #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 > #include > #include > +#include > #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 > #include > #include > +#include >=20=20 > #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 > #include > #include > +#include > #include "ext4.h" > #include "ext4_jbd2.h" >=20=20 > 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 /* for inode_has_buffers */ > #include > #include > +#include > #include > #include "internal.h" >=20=20 > 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 ino= de *inode) > mark_inode_dirty(inode); > } >=20=20 > -/** > - * 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 increme= nted. > - * 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 =3D 1, > S_MTIME =3D 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 > + > +/* > + * The change attribute (i_version) is mandated by NFSv4 and is mostly f= or > + * 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 da= ta or > + * metadata since it was last queried. > + * > + * It should be considered an opaque value by observers. If it remains t= he 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. Subsyst= ems 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 m= acro). > + * > + * Those that set SB_I_VERSION will automatically have their i_version c= ounter > + * 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 ho= w it > + * wishes. Note that the filesystem is always responsible for updating t= he > + * i_version on namespace changes in directories (mkdir, rmdir, unlink, = etc.). > + * We consider these sorts of filesystems to have a kernel-managed i_ver= sion. > + * > + * Note that some filesystems (e.g. NFS and AFS) just use the field to s= tore > + * 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 =3D 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 filesystem= s 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. Thu= s, 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 v= alue > + * 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_loc= k 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 chan= ge 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 increment= ed? > + * @inode: inode to check > + * > + * Returns whether the inode->i_version counter needs incrementing on th= e 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 n= ot > + * 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 increm= ented > + * @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_v= ersion > + * on disk. In that situation, it's not necessary to flag it as having b= een > + * 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 guara= ntee > + * 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 a= re > + * 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 > --=20 > 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 --=-=-= Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQIzBAEBCAAdFiEEG8Yp69OQ2HB7X0l6Oeye3VZigbkFAlo9kcsACgkQOeye3VZi gbkteQ/9HWUFYQFS7GfJm491MWt9JgBJ2ISsVIvCnw91XkEfJwkh7LalCUp006aa 6RjkNR/y1HKeDg76DK2l0BvcPgtG2mMPOeknM0bP0agQMduGNM7HR4KuT07w0Ykx aoykya7T2WhROoD0dD0GSMG8ZHMzXyta6pfQVY+LEkdthS/6jckR/ZBglt4unUET ffrFikuvKp1Kd6Iy3qDUcfL4bqV7UbqAUHMULA51XGmgLIz0CEOqX62rADkl7+Do g8GdcIOjef6wIWAZjBGwzoH5lnp3urgolB/BKlt8pZYZ2AMZrhmFzhJPX2XY4rZQ +Fi84TWpyj5+kB1Q4Q6rLKAAbAQRMZ56uecIhz7neFJp97ZlUXXBzy7FyN3y6hEC wMTotmvnq6Fsh1EIMjIEvDJByALU6IIsvFCm2tG41Rm0nkZH+emhjDK4D7iTUuad q2OfT6L92TUs1YYhnPN0cefMFSRyRfvzSRRPOtia/C3IZ12IWAykY8heEMigpuw8 Q1TC17H0Yl0U8u4IBb2hfS/FJi91pFfP5Pta00KWLr8XkQPqz2IS4eqYgC5/a+Sx J4UVucyAAr0AgRLM+rzMq2j/qEUwvDzwXhUxIANMUd8W9hWTE+1DQbT8hU/A2h// CNT7VtBfywPOFyb6HgXpQXRkjKw/CLTnvdj+4tRgI1tiXCSgnWQ= =UWMg -----END PGP SIGNATURE----- --=-=-=--