diff options
| -rw-r--r-- | Documentation/filesystems/locking.rst | 8 | ||||
| -rw-r--r-- | Documentation/filesystems/vfs.rst | 6 | ||||
| -rw-r--r-- | fs/libfs.c | 248 | ||||
| -rw-r--r-- | include/linux/fs.h | 18 |
4 files changed, 276 insertions, 4 deletions
diff --git a/Documentation/filesystems/locking.rst b/Documentation/filesystems/locking.rst index ed148919e11a..443091406e35 100644 --- a/Documentation/filesystems/locking.rst +++ b/Documentation/filesystems/locking.rst @@ -85,13 +85,14 @@ prototypes:: struct dentry *dentry, struct fileattr *fa); int (*fileattr_get)(struct dentry *dentry, struct fileattr *fa); struct posix_acl * (*get_acl)(struct mnt_idmap *, struct dentry *, int); + struct offset_ctx *(*get_offset_ctx)(struct inode *inode); locking rules: all may block -============== ============================================= +============== ================================================== ops i_rwsem(inode) -============== ============================================= +============== ================================================== lookup: shared create: exclusive link: exclusive (both) @@ -115,7 +116,8 @@ atomic_open: shared (exclusive if O_CREAT is set in open flags) tmpfile: no fileattr_get: no or exclusive fileattr_set: exclusive -============== ============================================= +get_offset_ctx no +============== ================================================== Additionally, ->rmdir(), ->unlink() and ->rename() have ->i_rwsem diff --git a/Documentation/filesystems/vfs.rst b/Documentation/filesystems/vfs.rst index cb2a97e49872..898d0b43109e 100644 --- a/Documentation/filesystems/vfs.rst +++ b/Documentation/filesystems/vfs.rst @@ -515,6 +515,7 @@ As of kernel 2.6.22, the following members are defined: 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); }; Again, all methods are called without any locks being held, unless @@ -675,7 +676,10 @@ otherwise noted. called on ioctl(FS_IOC_SETFLAGS) and ioctl(FS_IOC_FSSETXATTR) to change miscellaneous file flags and attributes. Callers hold i_rwsem exclusive. If unset, then fall back to f_op->ioctl(). - +``get_offset_ctx`` + called to get the offset context for a directory inode. A + filesystem must define this operation to use + simple_offset_dir_operations. The Address Space Object ======================== diff --git a/fs/libfs.c b/fs/libfs.c index 5b851315eeed..a7e56baf8bbd 100644 --- a/fs/libfs.c +++ b/fs/libfs.c @@ -239,6 +239,254 @@ const struct inode_operations simple_dir_inode_operations = { }; EXPORT_SYMBOL(simple_dir_inode_operations); +static void offset_set(struct dentry *dentry, u32 offset) +{ + dentry->d_fsdata = (void *)((uintptr_t)(offset)); +} + +static u32 dentry2offset(struct dentry *dentry) +{ + return (u32)((uintptr_t)(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) +{ + u32 offset; + + offset = dentry2offset(dentry); + if (offset == 0) + return; + + xa_erase(&octx->xa, offset); + 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); + u32 old_index = dentry2offset(old_dentry); + u32 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) +{ + u32 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 6867512907d6..59a4129ce14c 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -1770,6 +1770,7 @@ struct dir_context { struct iov_iter; struct io_uring_cmd; +struct offset_ctx; struct file_operations { struct module *owner; @@ -1857,6 +1858,7 @@ 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, @@ -2971,6 +2973,22 @@ 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); |