| Message ID | 168796590904.157221.11286772826871541854.stgit@manet.1015granger.net (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | shmemfs stable directory offsets | expand |
On 6/28/23 17:25, Chuck Lever wrote: > From: Chuck Lever <chuck.lever@oracle.com> > > Create a vector of directory operations in fs/libfs.c that handles > directory seeks and readdir via stable offsets instead of the > current cursor-based mechanism. > > For the moment these are unused. > > Signed-off-by: Chuck Lever <chuck.lever@oracle.com> > --- > fs/libfs.c | 247 ++++++++++++++++++++++++++++++++++++++++++++++++++++ > include/linux/fs.h | 18 ++++ > 2 files changed, 265 insertions(+) > > diff --git a/fs/libfs.c b/fs/libfs.c > index 89cf614a3271..2b0d5ac472df 100644 > --- a/fs/libfs.c > +++ b/fs/libfs.c > @@ -239,6 +239,253 @@ const struct inode_operations simple_dir_inode_operations = { > }; > EXPORT_SYMBOL(simple_dir_inode_operations); > > +static void offset_set(struct dentry *dentry, unsigned long offset) > +{ > + dentry->d_fsdata = (void *)offset; > +} > + > +static unsigned long dentry2offset(struct dentry *dentry) > +{ > + return (unsigned long)dentry->d_fsdata; > +} > + > +/** > + * simple_offset_init - initialize an offset_ctx > + * @octx: directory offset map to be initialized > + * > + */ > +void simple_offset_init(struct offset_ctx *octx) > +{ > + xa_init_flags(&octx->xa, XA_FLAGS_ALLOC1); > + > + /* 0 is '.', 1 is '..', so always start with offset 2 */ > + octx->next_offset = 2; > +} > + > +/** > + * simple_offset_add - Add an entry to a directory's offset map > + * @octx: directory offset ctx to be updated > + * @dentry: new dentry being added > + * > + * Returns zero on success. @so_ctx and the dentry offset are updated. > + * Otherwise, a negative errno value is returned. > + */ > +int simple_offset_add(struct offset_ctx *octx, struct dentry *dentry) > +{ > + static const struct xa_limit limit = XA_LIMIT(2, U32_MAX); > + u32 offset; > + int ret; > + > + if (dentry2offset(dentry) != 0) > + return -EBUSY; > + > + ret = xa_alloc_cyclic(&octx->xa, &offset, dentry, limit, > + &octx->next_offset, GFP_KERNEL); > + if (ret < 0) > + return ret; > + > + offset_set(dentry, offset); > + return 0; > +} > + > +/** > + * simple_offset_remove - Remove an entry to a directory's offset map > + * @octx: directory offset ctx to be updated > + * @dentry: dentry being removed > + * > + */ > +void simple_offset_remove(struct offset_ctx *octx, struct dentry *dentry) > +{ > + unsigned long index = dentry2offset(dentry); > + > + if (index == 0) > + return; > + > + xa_erase(&octx->xa, index); > + offset_set(dentry, 0); > +} > + > +/** > + * simple_offset_rename_exchange - exchange rename with directory offsets > + * @old_dir: parent of dentry being moved > + * @old_dentry: dentry being moved > + * @new_dir: destination parent > + * @new_dentry: destination dentry > + * > + * Returns zero on success. Otherwise a negative errno is returned and the > + * rename is rolled back. > + */ > +int simple_offset_rename_exchange(struct inode *old_dir, > + struct dentry *old_dentry, > + struct inode *new_dir, > + struct dentry *new_dentry) > +{ > + struct offset_ctx *old_ctx = old_dir->i_op->get_offset_ctx(old_dir); > + struct offset_ctx *new_ctx = new_dir->i_op->get_offset_ctx(new_dir); > + unsigned long old_index = dentry2offset(old_dentry); > + unsigned long new_index = dentry2offset(new_dentry); > + int ret; > + > + simple_offset_remove(old_ctx, old_dentry); > + simple_offset_remove(new_ctx, new_dentry); > + > + ret = simple_offset_add(new_ctx, old_dentry); > + if (ret) > + goto out_restore; > + > + ret = simple_offset_add(old_ctx, new_dentry); > + if (ret) { > + simple_offset_remove(new_ctx, old_dentry); > + goto out_restore; > + } > + > + ret = simple_rename_exchange(old_dir, old_dentry, new_dir, new_dentry); > + if (ret) { > + simple_offset_remove(new_ctx, old_dentry); > + simple_offset_remove(old_ctx, new_dentry); > + goto out_restore; > + } > + return 0; > + > +out_restore: > + offset_set(old_dentry, old_index); > + xa_store(&old_ctx->xa, old_index, old_dentry, GFP_KERNEL); > + offset_set(new_dentry, new_index); > + xa_store(&new_ctx->xa, new_index, new_dentry, GFP_KERNEL); > + return ret; > +} Thanks for the update, looks great! > + > +/** > + * simple_offset_destroy - Release offset map > + * @octx: directory offset ctx that is about to be destroyed > + * > + * During fs teardown (eg. umount), a directory's offset map might still > + * contain entries. xa_destroy() cleans out anything that remains. > + */ > +void simple_offset_destroy(struct offset_ctx *octx) > +{ > + xa_destroy(&octx->xa); > +} > + > +/** > + * offset_dir_llseek - Advance the read position of a directory descriptor > + * @file: an open directory whose position is to be updated > + * @offset: a byte offset > + * @whence: enumerator describing the starting position for this update > + * > + * SEEK_END, SEEK_DATA, and SEEK_HOLE are not supported for directories. > + * > + * Returns the updated read position if successful; otherwise a > + * negative errno is returned and the read position remains unchanged. > + */ > +static loff_t offset_dir_llseek(struct file *file, loff_t offset, int whence) > +{ > + switch (whence) { > + case SEEK_CUR: > + offset += file->f_pos; > + fallthrough; > + case SEEK_SET: > + if (offset >= 0) > + break; > + fallthrough; > + default: > + return -EINVAL; > + } > + > + return vfs_setpos(file, offset, U32_MAX); > +} > + > +static struct dentry *offset_find_next(struct xa_state *xas) > +{ > + struct dentry *child, *found = NULL; > + > + rcu_read_lock(); > + child = xas_next_entry(xas, U32_MAX); > + if (!child) > + goto out; > + spin_lock_nested(&child->d_lock, DENTRY_D_LOCK_NESTED); > + if (simple_positive(child)) > + found = dget_dlock(child); > + spin_unlock(&child->d_lock); > +out: > + rcu_read_unlock(); > + return found; > +} > + > +static bool offset_dir_emit(struct dir_context *ctx, struct dentry *dentry) > +{ > + loff_t offset = dentry2offset(dentry); > + struct inode *inode = d_inode(dentry); > + > + return ctx->actor(ctx, dentry->d_name.name, dentry->d_name.len, offset, > + inode->i_ino, fs_umode_to_dtype(inode->i_mode)); > +} > + > +static void offset_iterate_dir(struct dentry *dir, struct dir_context *ctx) > +{ > + struct inode *inode = d_inode(dir); > + struct offset_ctx *so_ctx = inode->i_op->get_offset_ctx(inode); > + XA_STATE(xas, &so_ctx->xa, ctx->pos); > + struct dentry *dentry; > + > + while (true) { > + spin_lock(&dir->d_lock); > + dentry = offset_find_next(&xas); > + spin_unlock(&dir->d_lock); > + if (!dentry) > + break; > + > + if (!offset_dir_emit(ctx, dentry)) { > + dput(dentry); > + break; > + } > + > + dput(dentry); > + ctx->pos = xas.xa_index + 1; > + } > +} > + > +/** > + * offset_readdir - Emit entries starting at offset @ctx->pos > + * @file: an open directory to iterate over > + * @ctx: directory iteration context > + * > + * Caller must hold @file's i_rwsem to prevent insertion or removal of > + * entries during this call. > + * > + * On entry, @ctx->pos contains an offset that represents the first entry > + * to be read from the directory. > + * > + * The operation continues until there are no more entries to read, or > + * until the ctx->actor indicates there is no more space in the caller's > + * output buffer. > + * > + * On return, @ctx->pos contains an offset that will read the next entry > + * in this directory when shmem_readdir() is called again with @ctx. > + * > + * Return values: > + * %0 - Complete > + */ > +static int offset_readdir(struct file *file, struct dir_context *ctx) > +{ > + struct dentry *dir = file->f_path.dentry; > + > + lockdep_assert_held(&d_inode(dir)->i_rwsem); > + > + if (!dir_emit_dots(file, ctx)) > + return 0; > + > + offset_iterate_dir(dir, ctx); > + return 0; > +} > + > +const struct file_operations simple_offset_dir_operations = { > + .llseek = offset_dir_llseek, > + .iterate_shared = offset_readdir, > + .read = generic_read_dir, > + .fsync = noop_fsync, > +}; > + > static struct dentry *find_next_child(struct dentry *parent, struct dentry *prev) > { > struct dentry *child = NULL; > diff --git a/include/linux/fs.h b/include/linux/fs.h > index 133f0640fb24..85de389e4eb8 100644 > --- a/include/linux/fs.h > +++ b/include/linux/fs.h > @@ -1767,6 +1767,7 @@ struct dir_context { > > struct iov_iter; > struct io_uring_cmd; > +struct offset_ctx; > > struct file_operations { > struct module *owner; > @@ -1854,6 +1855,7 @@ struct inode_operations { > int (*fileattr_set)(struct mnt_idmap *idmap, > struct dentry *dentry, struct fileattr *fa); > int (*fileattr_get)(struct dentry *dentry, struct fileattr *fa); > + struct offset_ctx *(*get_offset_ctx)(struct inode *inode); > } ____cacheline_aligned; Should this be documented in filesystems/vfs.rst and filesystems/locking.rst? Thanks, Bernd
diff --git a/fs/libfs.c b/fs/libfs.c index 89cf614a3271..2b0d5ac472df 100644 --- a/fs/libfs.c +++ b/fs/libfs.c @@ -239,6 +239,253 @@ const struct inode_operations simple_dir_inode_operations = { }; EXPORT_SYMBOL(simple_dir_inode_operations); +static void offset_set(struct dentry *dentry, unsigned long offset) +{ + dentry->d_fsdata = (void *)offset; +} + +static unsigned long dentry2offset(struct dentry *dentry) +{ + return (unsigned long)dentry->d_fsdata; +} + +/** + * simple_offset_init - initialize an offset_ctx + * @octx: directory offset map to be initialized + * + */ +void simple_offset_init(struct offset_ctx *octx) +{ + xa_init_flags(&octx->xa, XA_FLAGS_ALLOC1); + + /* 0 is '.', 1 is '..', so always start with offset 2 */ + octx->next_offset = 2; +} + +/** + * simple_offset_add - Add an entry to a directory's offset map + * @octx: directory offset ctx to be updated + * @dentry: new dentry being added + * + * Returns zero on success. @so_ctx and the dentry offset are updated. + * Otherwise, a negative errno value is returned. + */ +int simple_offset_add(struct offset_ctx *octx, struct dentry *dentry) +{ + static const struct xa_limit limit = XA_LIMIT(2, U32_MAX); + u32 offset; + int ret; + + if (dentry2offset(dentry) != 0) + return -EBUSY; + + ret = xa_alloc_cyclic(&octx->xa, &offset, dentry, limit, + &octx->next_offset, GFP_KERNEL); + if (ret < 0) + return ret; + + offset_set(dentry, offset); + return 0; +} + +/** + * simple_offset_remove - Remove an entry to a directory's offset map + * @octx: directory offset ctx to be updated + * @dentry: dentry being removed + * + */ +void simple_offset_remove(struct offset_ctx *octx, struct dentry *dentry) +{ + unsigned long index = dentry2offset(dentry); + + if (index == 0) + return; + + xa_erase(&octx->xa, index); + offset_set(dentry, 0); +} + +/** + * simple_offset_rename_exchange - exchange rename with directory offsets + * @old_dir: parent of dentry being moved + * @old_dentry: dentry being moved + * @new_dir: destination parent + * @new_dentry: destination dentry + * + * Returns zero on success. Otherwise a negative errno is returned and the + * rename is rolled back. + */ +int simple_offset_rename_exchange(struct inode *old_dir, + struct dentry *old_dentry, + struct inode *new_dir, + struct dentry *new_dentry) +{ + struct offset_ctx *old_ctx = old_dir->i_op->get_offset_ctx(old_dir); + struct offset_ctx *new_ctx = new_dir->i_op->get_offset_ctx(new_dir); + unsigned long old_index = dentry2offset(old_dentry); + unsigned long new_index = dentry2offset(new_dentry); + int ret; + + simple_offset_remove(old_ctx, old_dentry); + simple_offset_remove(new_ctx, new_dentry); + + ret = simple_offset_add(new_ctx, old_dentry); + if (ret) + goto out_restore; + + ret = simple_offset_add(old_ctx, new_dentry); + if (ret) { + simple_offset_remove(new_ctx, old_dentry); + goto out_restore; + } + + ret = simple_rename_exchange(old_dir, old_dentry, new_dir, new_dentry); + if (ret) { + simple_offset_remove(new_ctx, old_dentry); + simple_offset_remove(old_ctx, new_dentry); + goto out_restore; + } + return 0; + +out_restore: + offset_set(old_dentry, old_index); + xa_store(&old_ctx->xa, old_index, old_dentry, GFP_KERNEL); + offset_set(new_dentry, new_index); + xa_store(&new_ctx->xa, new_index, new_dentry, GFP_KERNEL); + return ret; +} + +/** + * simple_offset_destroy - Release offset map + * @octx: directory offset ctx that is about to be destroyed + * + * During fs teardown (eg. umount), a directory's offset map might still + * contain entries. xa_destroy() cleans out anything that remains. + */ +void simple_offset_destroy(struct offset_ctx *octx) +{ + xa_destroy(&octx->xa); +} + +/** + * offset_dir_llseek - Advance the read position of a directory descriptor + * @file: an open directory whose position is to be updated + * @offset: a byte offset + * @whence: enumerator describing the starting position for this update + * + * SEEK_END, SEEK_DATA, and SEEK_HOLE are not supported for directories. + * + * Returns the updated read position if successful; otherwise a + * negative errno is returned and the read position remains unchanged. + */ +static loff_t offset_dir_llseek(struct file *file, loff_t offset, int whence) +{ + switch (whence) { + case SEEK_CUR: + offset += file->f_pos; + fallthrough; + case SEEK_SET: + if (offset >= 0) + break; + fallthrough; + default: + return -EINVAL; + } + + return vfs_setpos(file, offset, U32_MAX); +} + +static struct dentry *offset_find_next(struct xa_state *xas) +{ + struct dentry *child, *found = NULL; + + rcu_read_lock(); + child = xas_next_entry(xas, U32_MAX); + if (!child) + goto out; + spin_lock_nested(&child->d_lock, DENTRY_D_LOCK_NESTED); + if (simple_positive(child)) + found = dget_dlock(child); + spin_unlock(&child->d_lock); +out: + rcu_read_unlock(); + return found; +} + +static bool offset_dir_emit(struct dir_context *ctx, struct dentry *dentry) +{ + loff_t offset = dentry2offset(dentry); + struct inode *inode = d_inode(dentry); + + return ctx->actor(ctx, dentry->d_name.name, dentry->d_name.len, offset, + inode->i_ino, fs_umode_to_dtype(inode->i_mode)); +} + +static void offset_iterate_dir(struct dentry *dir, struct dir_context *ctx) +{ + struct inode *inode = d_inode(dir); + struct offset_ctx *so_ctx = inode->i_op->get_offset_ctx(inode); + XA_STATE(xas, &so_ctx->xa, ctx->pos); + struct dentry *dentry; + + while (true) { + spin_lock(&dir->d_lock); + dentry = offset_find_next(&xas); + spin_unlock(&dir->d_lock); + if (!dentry) + break; + + if (!offset_dir_emit(ctx, dentry)) { + dput(dentry); + break; + } + + dput(dentry); + ctx->pos = xas.xa_index + 1; + } +} + +/** + * offset_readdir - Emit entries starting at offset @ctx->pos + * @file: an open directory to iterate over + * @ctx: directory iteration context + * + * Caller must hold @file's i_rwsem to prevent insertion or removal of + * entries during this call. + * + * On entry, @ctx->pos contains an offset that represents the first entry + * to be read from the directory. + * + * The operation continues until there are no more entries to read, or + * until the ctx->actor indicates there is no more space in the caller's + * output buffer. + * + * On return, @ctx->pos contains an offset that will read the next entry + * in this directory when shmem_readdir() is called again with @ctx. + * + * Return values: + * %0 - Complete + */ +static int offset_readdir(struct file *file, struct dir_context *ctx) +{ + struct dentry *dir = file->f_path.dentry; + + lockdep_assert_held(&d_inode(dir)->i_rwsem); + + if (!dir_emit_dots(file, ctx)) + return 0; + + offset_iterate_dir(dir, ctx); + return 0; +} + +const struct file_operations simple_offset_dir_operations = { + .llseek = offset_dir_llseek, + .iterate_shared = offset_readdir, + .read = generic_read_dir, + .fsync = noop_fsync, +}; + static struct dentry *find_next_child(struct dentry *parent, struct dentry *prev) { struct dentry *child = NULL; diff --git a/include/linux/fs.h b/include/linux/fs.h index 133f0640fb24..85de389e4eb8 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -1767,6 +1767,7 @@ struct dir_context { struct iov_iter; struct io_uring_cmd; +struct offset_ctx; struct file_operations { struct module *owner; @@ -1854,6 +1855,7 @@ struct inode_operations { int (*fileattr_set)(struct mnt_idmap *idmap, struct dentry *dentry, struct fileattr *fa); int (*fileattr_get)(struct dentry *dentry, struct fileattr *fa); + struct offset_ctx *(*get_offset_ctx)(struct inode *inode); } ____cacheline_aligned; static inline ssize_t call_read_iter(struct file *file, struct kiocb *kio, @@ -2954,6 +2956,22 @@ extern ssize_t simple_read_from_buffer(void __user *to, size_t count, extern ssize_t simple_write_to_buffer(void *to, size_t available, loff_t *ppos, const void __user *from, size_t count); +struct offset_ctx { + struct xarray xa; + u32 next_offset; +}; + +void simple_offset_init(struct offset_ctx *octx); +int simple_offset_add(struct offset_ctx *octx, struct dentry *dentry); +void simple_offset_remove(struct offset_ctx *octx, struct dentry *dentry); +int simple_offset_rename_exchange(struct inode *old_dir, + struct dentry *old_dentry, + struct inode *new_dir, + struct dentry *new_dentry); +void simple_offset_destroy(struct offset_ctx *octx); + +extern const struct file_operations simple_offset_dir_operations; + extern int __generic_file_fsync(struct file *, loff_t, loff_t, int); extern int generic_file_fsync(struct file *, loff_t, loff_t, int);