libfs: Add directory operations for stable offsets
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> Message-Id: <168814732984.530310.11190772066786107220.stgit@manet.1015granger.net> Signed-off-by: Christian Brauner <brauner@kernel.org>
This commit is contained in:
Chuck Lever
Christian Brauner
parent
509f006932
commit
6faddda69f
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@ -85,13 +85,14 @@ prototypes::
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struct dentry *dentry, struct fileattr *fa);
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int (*fileattr_get)(struct dentry *dentry, struct fileattr *fa);
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struct posix_acl * (*get_acl)(struct mnt_idmap *, struct dentry *, int);
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struct offset_ctx *(*get_offset_ctx)(struct inode *inode);
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locking rules:
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all may block
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============== =============================================
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============== ==================================================
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ops i_rwsem(inode)
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============== =============================================
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============== ==================================================
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lookup: shared
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create: exclusive
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link: exclusive (both)
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@ -115,7 +116,8 @@ atomic_open: shared (exclusive if O_CREAT is set in open flags)
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tmpfile: no
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fileattr_get: no or exclusive
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fileattr_set: exclusive
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============== =============================================
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get_offset_ctx no
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============== ==================================================
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Additionally, ->rmdir(), ->unlink() and ->rename() have ->i_rwsem
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@ -515,6 +515,7 @@ As of kernel 2.6.22, the following members are defined:
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int (*fileattr_set)(struct mnt_idmap *idmap,
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struct dentry *dentry, struct fileattr *fa);
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int (*fileattr_get)(struct dentry *dentry, struct fileattr *fa);
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struct offset_ctx *(*get_offset_ctx)(struct inode *inode);
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};
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Again, all methods are called without any locks being held, unless
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@ -675,7 +676,10 @@ otherwise noted.
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called on ioctl(FS_IOC_SETFLAGS) and ioctl(FS_IOC_FSSETXATTR) to
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change miscellaneous file flags and attributes. Callers hold
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i_rwsem exclusive. If unset, then fall back to f_op->ioctl().
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``get_offset_ctx``
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called to get the offset context for a directory inode. A
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filesystem must define this operation to use
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simple_offset_dir_operations.
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The Address Space Object
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========================
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248
fs/libfs.c
248
fs/libfs.c
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@ -239,6 +239,254 @@ const struct inode_operations simple_dir_inode_operations = {
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};
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EXPORT_SYMBOL(simple_dir_inode_operations);
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static void offset_set(struct dentry *dentry, u32 offset)
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{
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dentry->d_fsdata = (void *)((uintptr_t)(offset));
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}
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static u32 dentry2offset(struct dentry *dentry)
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{
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return (u32)((uintptr_t)(dentry->d_fsdata));
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}
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/**
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* simple_offset_init - initialize an offset_ctx
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* @octx: directory offset map to be initialized
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*
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*/
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void simple_offset_init(struct offset_ctx *octx)
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{
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xa_init_flags(&octx->xa, XA_FLAGS_ALLOC1);
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/* 0 is '.', 1 is '..', so always start with offset 2 */
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octx->next_offset = 2;
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}
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/**
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* simple_offset_add - Add an entry to a directory's offset map
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* @octx: directory offset ctx to be updated
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* @dentry: new dentry being added
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*
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* Returns zero on success. @so_ctx and the dentry offset are updated.
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* Otherwise, a negative errno value is returned.
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*/
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int simple_offset_add(struct offset_ctx *octx, struct dentry *dentry)
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{
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static const struct xa_limit limit = XA_LIMIT(2, U32_MAX);
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u32 offset;
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int ret;
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if (dentry2offset(dentry) != 0)
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return -EBUSY;
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ret = xa_alloc_cyclic(&octx->xa, &offset, dentry, limit,
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&octx->next_offset, GFP_KERNEL);
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if (ret < 0)
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return ret;
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offset_set(dentry, offset);
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return 0;
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}
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/**
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* simple_offset_remove - Remove an entry to a directory's offset map
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* @octx: directory offset ctx to be updated
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* @dentry: dentry being removed
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*
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*/
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void simple_offset_remove(struct offset_ctx *octx, struct dentry *dentry)
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{
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u32 offset;
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offset = dentry2offset(dentry);
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if (offset == 0)
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return;
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xa_erase(&octx->xa, offset);
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offset_set(dentry, 0);
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}
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/**
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* simple_offset_rename_exchange - exchange rename with directory offsets
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* @old_dir: parent of dentry being moved
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* @old_dentry: dentry being moved
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* @new_dir: destination parent
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* @new_dentry: destination dentry
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*
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* Returns zero on success. Otherwise a negative errno is returned and the
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* rename is rolled back.
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*/
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int simple_offset_rename_exchange(struct inode *old_dir,
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struct dentry *old_dentry,
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struct inode *new_dir,
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struct dentry *new_dentry)
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{
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struct offset_ctx *old_ctx = old_dir->i_op->get_offset_ctx(old_dir);
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struct offset_ctx *new_ctx = new_dir->i_op->get_offset_ctx(new_dir);
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u32 old_index = dentry2offset(old_dentry);
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u32 new_index = dentry2offset(new_dentry);
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int ret;
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simple_offset_remove(old_ctx, old_dentry);
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simple_offset_remove(new_ctx, new_dentry);
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ret = simple_offset_add(new_ctx, old_dentry);
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if (ret)
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goto out_restore;
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ret = simple_offset_add(old_ctx, new_dentry);
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if (ret) {
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simple_offset_remove(new_ctx, old_dentry);
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goto out_restore;
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}
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ret = simple_rename_exchange(old_dir, old_dentry, new_dir, new_dentry);
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if (ret) {
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simple_offset_remove(new_ctx, old_dentry);
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simple_offset_remove(old_ctx, new_dentry);
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goto out_restore;
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}
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return 0;
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out_restore:
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offset_set(old_dentry, old_index);
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xa_store(&old_ctx->xa, old_index, old_dentry, GFP_KERNEL);
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offset_set(new_dentry, new_index);
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xa_store(&new_ctx->xa, new_index, new_dentry, GFP_KERNEL);
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return ret;
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}
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/**
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* simple_offset_destroy - Release offset map
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* @octx: directory offset ctx that is about to be destroyed
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*
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* During fs teardown (eg. umount), a directory's offset map might still
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* contain entries. xa_destroy() cleans out anything that remains.
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*/
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void simple_offset_destroy(struct offset_ctx *octx)
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{
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xa_destroy(&octx->xa);
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}
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/**
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* offset_dir_llseek - Advance the read position of a directory descriptor
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* @file: an open directory whose position is to be updated
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* @offset: a byte offset
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* @whence: enumerator describing the starting position for this update
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*
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* SEEK_END, SEEK_DATA, and SEEK_HOLE are not supported for directories.
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*
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* Returns the updated read position if successful; otherwise a
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* negative errno is returned and the read position remains unchanged.
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*/
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static loff_t offset_dir_llseek(struct file *file, loff_t offset, int whence)
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{
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switch (whence) {
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case SEEK_CUR:
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offset += file->f_pos;
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fallthrough;
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case SEEK_SET:
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if (offset >= 0)
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break;
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fallthrough;
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default:
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return -EINVAL;
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}
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return vfs_setpos(file, offset, U32_MAX);
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}
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static struct dentry *offset_find_next(struct xa_state *xas)
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{
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struct dentry *child, *found = NULL;
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rcu_read_lock();
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child = xas_next_entry(xas, U32_MAX);
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if (!child)
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goto out;
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spin_lock_nested(&child->d_lock, DENTRY_D_LOCK_NESTED);
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if (simple_positive(child))
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found = dget_dlock(child);
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spin_unlock(&child->d_lock);
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out:
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rcu_read_unlock();
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return found;
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}
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static bool offset_dir_emit(struct dir_context *ctx, struct dentry *dentry)
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{
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u32 offset = dentry2offset(dentry);
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struct inode *inode = d_inode(dentry);
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return ctx->actor(ctx, dentry->d_name.name, dentry->d_name.len, offset,
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inode->i_ino, fs_umode_to_dtype(inode->i_mode));
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}
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static void offset_iterate_dir(struct dentry *dir, struct dir_context *ctx)
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{
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struct inode *inode = d_inode(dir);
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struct offset_ctx *so_ctx = inode->i_op->get_offset_ctx(inode);
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XA_STATE(xas, &so_ctx->xa, ctx->pos);
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struct dentry *dentry;
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while (true) {
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spin_lock(&dir->d_lock);
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dentry = offset_find_next(&xas);
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spin_unlock(&dir->d_lock);
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if (!dentry)
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break;
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if (!offset_dir_emit(ctx, dentry)) {
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dput(dentry);
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break;
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}
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dput(dentry);
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ctx->pos = xas.xa_index + 1;
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}
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}
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/**
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* offset_readdir - Emit entries starting at offset @ctx->pos
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* @file: an open directory to iterate over
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* @ctx: directory iteration context
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*
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* Caller must hold @file's i_rwsem to prevent insertion or removal of
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* entries during this call.
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*
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* On entry, @ctx->pos contains an offset that represents the first entry
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* to be read from the directory.
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*
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* The operation continues until there are no more entries to read, or
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* until the ctx->actor indicates there is no more space in the caller's
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* output buffer.
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*
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* On return, @ctx->pos contains an offset that will read the next entry
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* in this directory when shmem_readdir() is called again with @ctx.
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*
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* Return values:
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* %0 - Complete
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*/
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static int offset_readdir(struct file *file, struct dir_context *ctx)
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{
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struct dentry *dir = file->f_path.dentry;
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lockdep_assert_held(&d_inode(dir)->i_rwsem);
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if (!dir_emit_dots(file, ctx))
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return 0;
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offset_iterate_dir(dir, ctx);
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return 0;
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}
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const struct file_operations simple_offset_dir_operations = {
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.llseek = offset_dir_llseek,
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.iterate_shared = offset_readdir,
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.read = generic_read_dir,
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.fsync = noop_fsync,
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};
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static struct dentry *find_next_child(struct dentry *parent, struct dentry *prev)
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{
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struct dentry *child = NULL;
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@ -1770,6 +1770,7 @@ struct dir_context {
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struct iov_iter;
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struct io_uring_cmd;
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struct offset_ctx;
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struct file_operations {
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struct module *owner;
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@ -1857,6 +1858,7 @@ struct inode_operations {
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int (*fileattr_set)(struct mnt_idmap *idmap,
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struct dentry *dentry, struct fileattr *fa);
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int (*fileattr_get)(struct dentry *dentry, struct fileattr *fa);
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struct offset_ctx *(*get_offset_ctx)(struct inode *inode);
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} ____cacheline_aligned;
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static inline ssize_t call_read_iter(struct file *file, struct kiocb *kio,
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@ -2971,6 +2973,22 @@ extern ssize_t simple_read_from_buffer(void __user *to, size_t count,
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extern ssize_t simple_write_to_buffer(void *to, size_t available, loff_t *ppos,
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const void __user *from, size_t count);
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struct offset_ctx {
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struct xarray xa;
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u32 next_offset;
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};
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void simple_offset_init(struct offset_ctx *octx);
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int simple_offset_add(struct offset_ctx *octx, struct dentry *dentry);
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void simple_offset_remove(struct offset_ctx *octx, struct dentry *dentry);
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int simple_offset_rename_exchange(struct inode *old_dir,
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struct dentry *old_dentry,
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struct inode *new_dir,
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struct dentry *new_dentry);
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void simple_offset_destroy(struct offset_ctx *octx);
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extern const struct file_operations simple_offset_dir_operations;
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extern int __generic_file_fsync(struct file *, loff_t, loff_t, int);
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extern int generic_file_fsync(struct file *, loff_t, loff_t, int);
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