| Message ID | 20171218151156.14565-2-jlayton@kernel.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Mon, 2017-12-18 at 10:11 -0500, 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> > --- > include/linux/fs.h | 15 ---- > include/linux/iversion.h | 205 +++++++++++++++++++++++++++++++++++++++++++++++ > 2 files changed, 205 insertions(+), 15 deletions(-) > create mode 100644 include/linux/iversion.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); > -} > - Note that this patch is broken, as I neglected to include linux/iversion.h in the files with the existing callers of inode_inc_iversion. Fixed in my in-tree version. > 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
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