Carved up FileSystem.
Aaron Jacobs
parent
8e746f35b5
commit
386855c559
476
fuseops/ops.go
476
fuseops/ops.go
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@ -23,278 +23,248 @@ import (
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"time"
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"github.com/jacobsa/bazilfuse"
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"golang.org/x/net/context"
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)
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// An interface that must be implemented by file systems to be mounted with
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// FUSE. See also the comments on request and response structs.
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// This method is called once when mounting the file system. It must succeed
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// in order for the mount to succeed.
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type InitOp struct {
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}
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////////////////////////////////////////////////////////////////////////
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// Inodes
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////////////////////////////////////////////////////////////////////////
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// Look up a child by name within a parent directory. The kernel calls this
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// when resolving user paths to dentry structs, which are then cached.
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type LookUpInodeOp struct {
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}
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// Refresh the attributes for an inode whose ID was previously returned by
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// LookUpInode. The kernel calls this when the FUSE VFS layer's cache of
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// inode attributes is stale. This is controlled by the AttributesExpiration
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// field of responses to LookUp, etc.
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type GetInodeAttributesOp struct {
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}
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// Change attributes for an inode.
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//
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// Not all methods need to have interesting implementations. Embed a field of
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// type fuseutil.NotImplementedFileSystem to inherit defaults that return
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// ENOSYS to the kernel.
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// The kernel calls this for obvious cases like chmod(2), and for less
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// obvious cases like ftrunctate(2).
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type SetInodeAttributesOp struct {
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}
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// Forget an inode ID previously issued (e.g. by LookUpInode or MkDir). The
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// kernel calls this when removing an inode from its internal caches.
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type ForgetInodeOp struct {
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}
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////////////////////////////////////////////////////////////////////////
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// Inode creation
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////////////////////////////////////////////////////////////////////////
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// Create a directory inode as a child of an existing directory inode. The
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// kernel sends this in response to a mkdir(2) call.
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//
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// Must be safe for concurrent access via all methods.
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type FileSystem interface {
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// This method is called once when mounting the file system. It must succeed
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// in order for the mount to succeed.
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Init(
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ctx context.Context,
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req *InitRequest) (*InitResponse, error)
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// The kernel appears to verify the name doesn't already exist (mkdir calls
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// mkdirat calls user_path_create calls filename_create, which verifies:
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// http://goo.gl/FZpLu5). But volatile file systems and paranoid non-volatile
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// file systems should check for the reasons described below on CreateFile.
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type MkDirOp struct {
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}
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///////////////////////////////////
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// Inodes
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///////////////////////////////////
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// Create a file inode and open it.
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//
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// The kernel calls this method when the user asks to open a file with the
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// O_CREAT flag and the kernel has observed that the file doesn't exist. (See
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// for example lookup_open, http://goo.gl/PlqE9d).
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//
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// However it's impossible to tell for sure that all kernels make this check
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// in all cases and the official fuse documentation is less than encouraging
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// (" the file does not exist, first create it with the specified mode, and
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// then open it"). Therefore file systems would be smart to be paranoid and
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// check themselves, returning EEXIST when the file already exists. This of
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// course particularly applies to file systems that are volatile from the
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// kernel's point of view.
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type CreateFileOp struct {
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}
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// Look up a child by name within a parent directory. The kernel calls this
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// when resolving user paths to dentry structs, which are then cached.
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LookUpInode(
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ctx context.Context,
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req *LookUpInodeRequest) (*LookUpInodeResponse, error)
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////////////////////////////////////////////////////////////////////////
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// Unlinking
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////////////////////////////////////////////////////////////////////////
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// Refresh the attributes for an inode whose ID was previously returned by
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// LookUpInode. The kernel calls this when the FUSE VFS layer's cache of
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// inode attributes is stale. This is controlled by the AttributesExpiration
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// field of responses to LookUp, etc.
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GetInodeAttributes(
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ctx context.Context,
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req *GetInodeAttributesRequest) (*GetInodeAttributesResponse, error)
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// Unlink a directory from its parent. Because directories cannot have a link
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// count above one, this means the directory inode should be deleted as well
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// once the kernel calls ForgetInode.
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//
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// The file system is responsible for checking that the directory is empty.
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//
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// Sample implementation in ext2: ext2_rmdir (http://goo.gl/B9QmFf)
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type RmDirOp struct {
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}
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// Change attributes for an inode.
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//
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// The kernel calls this for obvious cases like chmod(2), and for less
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// obvious cases like ftrunctate(2).
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SetInodeAttributes(
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ctx context.Context,
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req *SetInodeAttributesRequest) (*SetInodeAttributesResponse, error)
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// Unlink a file from its parent. If this brings the inode's link count to
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// zero, the inode should be deleted once the kernel calls ForgetInode. It
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// may still be referenced before then if a user still has the file open.
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//
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// Sample implementation in ext2: ext2_unlink (http://goo.gl/hY6r6C)
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type UnlinkOp struct {
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}
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// Forget an inode ID previously issued (e.g. by LookUpInode or MkDir). The
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// kernel calls this when removing an inode from its internal caches.
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ForgetInode(
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ctx context.Context,
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req *ForgetInodeRequest) (*ForgetInodeResponse, error)
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////////////////////////////////////////////////////////////////////////
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// Directory handles
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////////////////////////////////////////////////////////////////////////
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///////////////////////////////////
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// Inode creation
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///////////////////////////////////
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// Open a directory inode.
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//
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// On Linux the kernel calls this method when setting up a struct file for a
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// particular inode with type directory, usually in response to an open(2)
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// call from a user-space process. On OS X it may not be called for every
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// open(2) (cf. https://github.com/osxfuse/osxfuse/issues/199).
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type OpenDirOp struct {
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}
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// Create a directory inode as a child of an existing directory inode. The
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// kernel sends this in response to a mkdir(2) call.
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//
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// The kernel appears to verify the name doesn't already exist (mkdir calls
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// mkdirat calls user_path_create calls filename_create, which verifies:
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// http://goo.gl/FZpLu5). But volatile file systems and paranoid non-volatile
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// file systems should check for the reasons described below on CreateFile.
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MkDir(
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ctx context.Context,
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req *MkDirRequest) (*MkDirResponse, error)
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// Read entries from a directory previously opened with OpenDir.
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type ReadDirOp struct {
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}
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// Create a file inode and open it.
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//
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// The kernel calls this method when the user asks to open a file with the
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// O_CREAT flag and the kernel has observed that the file doesn't exist. (See
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// for example lookup_open, http://goo.gl/PlqE9d).
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//
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// However it's impossible to tell for sure that all kernels make this check
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// in all cases and the official fuse documentation is less than encouraging
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// (" the file does not exist, first create it with the specified mode, and
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// then open it"). Therefore file systems would be smart to be paranoid and
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// check themselves, returning EEXIST when the file already exists. This of
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// course particularly applies to file systems that are volatile from the
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// kernel's point of view.
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CreateFile(
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ctx context.Context,
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req *CreateFileRequest) (*CreateFileResponse, error)
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// Release a previously-minted directory handle. The kernel calls this when
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// there are no more references to an open directory: all file descriptors
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// are closed and all memory mappings are unmapped.
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//
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// The kernel guarantees that the handle ID will not be used in further calls
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// to the file system (unless it is reissued by the file system).
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type ReleaseDirHandleOp struct {
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}
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///////////////////////////////////
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// Inode destruction
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///////////////////////////////////
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////////////////////////////////////////////////////////////////////////
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// File handles
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////////////////////////////////////////////////////////////////////////
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// Unlink a directory from its parent. Because directories cannot have a link
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// count above one, this means the directory inode should be deleted as well
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// once the kernel calls ForgetInode.
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//
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// The file system is responsible for checking that the directory is empty.
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//
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// Sample implementation in ext2: ext2_rmdir (http://goo.gl/B9QmFf)
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RmDir(
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ctx context.Context,
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req *RmDirRequest) (*RmDirResponse, error)
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// Open a file inode.
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//
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// On Linux the kernel calls this method when setting up a struct file for a
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// particular inode with type file, usually in response to an open(2) call
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// from a user-space process. On OS X it may not be called for every open(2)
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// (cf.https://github.com/osxfuse/osxfuse/issues/199).
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type OpenFileOp struct {
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}
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// Unlink a file from its parent. If this brings the inode's link count to
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// zero, the inode should be deleted once the kernel calls ForgetInode. It
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// may still be referenced before then if a user still has the file open.
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//
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// Sample implementation in ext2: ext2_unlink (http://goo.gl/hY6r6C)
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Unlink(
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ctx context.Context,
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req *UnlinkRequest) (*UnlinkResponse, error)
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// Read data from a file previously opened with CreateFile or OpenFile.
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//
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// Note that this method is not called for every call to read(2) by the end
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// user; some reads may be served by the page cache. See notes on Write for
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// more.
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type ReadFileOp struct {
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}
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///////////////////////////////////
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// Directory handles
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///////////////////////////////////
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// Write data to a file previously opened with CreateFile or OpenFile.
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//
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// When the user writes data using write(2), the write goes into the page
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// cache and the page is marked dirty. Later the kernel may write back the
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// page via the FUSE VFS layer, causing this method to be called:
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//
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// * The kernel calls address_space_operations::writepage when a dirty page
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// needs to be written to backing store (cf. http://goo.gl/Ezbewg). Fuse
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// sets this to fuse_writepage (cf. http://goo.gl/IeNvLT).
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//
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// * (http://goo.gl/Eestuy) fuse_writepage calls fuse_writepage_locked.
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//
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// * (http://goo.gl/RqYIxY) fuse_writepage_locked makes a write request to
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// the userspace server.
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//
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// Note that writes *will* be received before a call to Flush when closing
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// the file descriptor to which they were written:
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//
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// * (http://goo.gl/PheZjf) fuse_flush calls write_inode_now, which appears
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// to start a writeback in the background (it talks about a "flusher
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// thread").
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//
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// * (http://goo.gl/1IiepM) fuse_flush then calls fuse_sync_writes, which
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// "[waits] for all pending writepages on the inode to finish".
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//
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// * (http://goo.gl/zzvxWv) Only then does fuse_flush finally send the
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// flush request.
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//
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type WriteFileOp struct {
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}
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// Open a directory inode.
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//
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// On Linux the kernel calls this method when setting up a struct file for a
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// particular inode with type directory, usually in response to an open(2)
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// call from a user-space process. On OS X it may not be called for every
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// open(2) (cf. https://github.com/osxfuse/osxfuse/issues/199).
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OpenDir(
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ctx context.Context,
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req *OpenDirRequest) (*OpenDirResponse, error)
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// Synchronize the current contents of an open file to storage.
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//
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// vfs.txt documents this as being called for by the fsync(2) system call
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// (cf. http://goo.gl/j9X8nB). Code walk for that case:
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//
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// * (http://goo.gl/IQkWZa) sys_fsync calls do_fsync, calls vfs_fsync, calls
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// vfs_fsync_range.
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//
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// * (http://goo.gl/5L2SMy) vfs_fsync_range calls f_op->fsync.
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//
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// Note that this is also called by fdatasync(2) (cf. http://goo.gl/01R7rF),
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// and may be called for msync(2) with the MS_SYNC flag (see the notes on
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// FlushFile).
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//
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// See also: FlushFile, which may perform a similar purpose when closing a
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// file (but which is not used in "real" file systems).
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type SyncFileOp struct {
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}
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// Read entries from a directory previously opened with OpenDir.
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ReadDir(
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ctx context.Context,
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req *ReadDirRequest) (*ReadDirResponse, error)
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// Flush the current state of an open file to storage upon closing a file
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// descriptor.
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//
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// vfs.txt documents this as being called for each close(2) system call (cf.
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// http://goo.gl/FSkbrq). Code walk for that case:
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//
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// * (http://goo.gl/e3lv0e) sys_close calls __close_fd, calls filp_close.
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// * (http://goo.gl/nI8fxD) filp_close calls f_op->flush (fuse_flush).
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//
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// But note that this is also called in other contexts where a file
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// descriptor is closed, such as dup2(2) (cf. http://goo.gl/NQDvFS). In the
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// case of close(2), a flush error is returned to the user. For dup2(2), it
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// is not.
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//
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// One potentially significant case where this may not be called is mmap'd
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// files, where the behavior is complicated:
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//
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// * munmap(2) does not cause flushes (cf. http://goo.gl/j8B9g0).
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//
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// * On OS X, if a user modifies a mapped file via the mapping before
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// closing the file with close(2), the WriteFile calls for the
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// modifications may not be received before the FlushFile request for the
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// close(2) (cf. http://goo.gl/kVmNcx).
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//
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// * However, even on OS X you can arrange for writes via a mapping to be
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// flushed by calling msync(2) followed by close(2). On OS X msync(2)
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// will cause a WriteFile to go through and close(2) will cause a
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// FlushFile as usual (cf. http://goo.gl/kVmNcx). On Linux, msync(2) does
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// nothing unless you set the MS_SYNC flag, in which case it causes a
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// SyncFile (cf. http://goo.gl/P3mErk).
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//
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// In summary: if you make data durable in both FlushFile and SyncFile, then
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// your users can get safe behavior from mapped files by calling msync(2)
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// with MS_SYNC, followed by munmap(2), followed by close(2). On Linux, the
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// msync(2) appears to be optional because close(2) implies dirty page
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// writeback (cf. http://goo.gl/HyzLTT).
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//
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// Because of cases like dup2(2), calls to FlushFile are not necessarily one
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// to one with calls to OpenFile. They should not be used for reference
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// counting, and the handle must remain valid even after the method is called
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// (use ReleaseFileHandle to dispose of it).
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//
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// Typical "real" file systems do not implement this, presumably relying on
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// the kernel to write out the page cache to the block device eventually.
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// They can get away with this because a later open(2) will see the same
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// data. A file system that writes to remote storage however probably wants
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// to at least schedule a real flush, and maybe do it immediately in order to
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// return any errors that occur.
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type FlushFileOp struct {
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}
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// Release a previously-minted directory handle. The kernel calls this when
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// there are no more references to an open directory: all file descriptors
|
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// are closed and all memory mappings are unmapped.
|
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//
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// The kernel guarantees that the handle ID will not be used in further calls
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// to the file system (unless it is reissued by the file system).
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ReleaseDirHandle(
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ctx context.Context,
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req *ReleaseDirHandleRequest) (*ReleaseDirHandleResponse, error)
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///////////////////////////////////
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// File handles
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///////////////////////////////////
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// Open a file inode.
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//
|
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// On Linux the kernel calls this method when setting up a struct file for a
|
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// particular inode with type file, usually in response to an open(2) call
|
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// from a user-space process. On OS X it may not be called for every open(2)
|
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// (cf.https://github.com/osxfuse/osxfuse/issues/199).
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OpenFile(
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ctx context.Context,
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req *OpenFileRequest) (*OpenFileResponse, error)
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// Read data from a file previously opened with CreateFile or OpenFile.
|
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//
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// Note that this method is not called for every call to read(2) by the end
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// user; some reads may be served by the page cache. See notes on Write for
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// more.
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ReadFile(
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ctx context.Context,
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req *ReadFileRequest) (*ReadFileResponse, error)
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// Write data to a file previously opened with CreateFile or OpenFile.
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//
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// When the user writes data using write(2), the write goes into the page
|
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// cache and the page is marked dirty. Later the kernel may write back the
|
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// page via the FUSE VFS layer, causing this method to be called:
|
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//
|
||||
// * The kernel calls address_space_operations::writepage when a dirty page
|
||||
// needs to be written to backing store (cf. http://goo.gl/Ezbewg). Fuse
|
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// sets this to fuse_writepage (cf. http://goo.gl/IeNvLT).
|
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//
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// * (http://goo.gl/Eestuy) fuse_writepage calls fuse_writepage_locked.
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//
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// * (http://goo.gl/RqYIxY) fuse_writepage_locked makes a write request to
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// the userspace server.
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//
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// Note that writes *will* be received before a call to Flush when closing
|
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// the file descriptor to which they were written:
|
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//
|
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// * (http://goo.gl/PheZjf) fuse_flush calls write_inode_now, which appears
|
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// to start a writeback in the background (it talks about a "flusher
|
||||
// thread").
|
||||
//
|
||||
// * (http://goo.gl/1IiepM) fuse_flush then calls fuse_sync_writes, which
|
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// "[waits] for all pending writepages on the inode to finish".
|
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//
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// * (http://goo.gl/zzvxWv) Only then does fuse_flush finally send the
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// flush request.
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//
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WriteFile(
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ctx context.Context,
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req *WriteFileRequest) (*WriteFileResponse, error)
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|
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// Synchronize the current contents of an open file to storage.
|
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//
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||||
// vfs.txt documents this as being called for by the fsync(2) system call
|
||||
// (cf. http://goo.gl/j9X8nB). Code walk for that case:
|
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//
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// * (http://goo.gl/IQkWZa) sys_fsync calls do_fsync, calls vfs_fsync, calls
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// vfs_fsync_range.
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//
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// * (http://goo.gl/5L2SMy) vfs_fsync_range calls f_op->fsync.
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//
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// Note that this is also called by fdatasync(2) (cf. http://goo.gl/01R7rF),
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// and may be called for msync(2) with the MS_SYNC flag (see the notes on
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// FlushFile).
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//
|
||||
// See also: FlushFile, which may perform a similar purpose when closing a
|
||||
// file (but which is not used in "real" file systems).
|
||||
SyncFile(
|
||||
ctx context.Context,
|
||||
req *SyncFileRequest) (*SyncFileResponse, error)
|
||||
|
||||
// Flush the current state of an open file to storage upon closing a file
|
||||
// descriptor.
|
||||
//
|
||||
// vfs.txt documents this as being called for each close(2) system call (cf.
|
||||
// http://goo.gl/FSkbrq). Code walk for that case:
|
||||
//
|
||||
// * (http://goo.gl/e3lv0e) sys_close calls __close_fd, calls filp_close.
|
||||
// * (http://goo.gl/nI8fxD) filp_close calls f_op->flush (fuse_flush).
|
||||
//
|
||||
// But note that this is also called in other contexts where a file
|
||||
// descriptor is closed, such as dup2(2) (cf. http://goo.gl/NQDvFS). In the
|
||||
// case of close(2), a flush error is returned to the user. For dup2(2), it
|
||||
// is not.
|
||||
//
|
||||
// One potentially significant case where this may not be called is mmap'd
|
||||
// files, where the behavior is complicated:
|
||||
//
|
||||
// * munmap(2) does not cause flushes (cf. http://goo.gl/j8B9g0).
|
||||
//
|
||||
// * On OS X, if a user modifies a mapped file via the mapping before
|
||||
// closing the file with close(2), the WriteFile calls for the
|
||||
// modifications may not be received before the FlushFile request for the
|
||||
// close(2) (cf. http://goo.gl/kVmNcx).
|
||||
//
|
||||
// * However, even on OS X you can arrange for writes via a mapping to be
|
||||
// flushed by calling msync(2) followed by close(2). On OS X msync(2)
|
||||
// will cause a WriteFile to go through and close(2) will cause a
|
||||
// FlushFile as usual (cf. http://goo.gl/kVmNcx). On Linux, msync(2) does
|
||||
// nothing unless you set the MS_SYNC flag, in which case it causes a
|
||||
// SyncFile (cf. http://goo.gl/P3mErk).
|
||||
//
|
||||
// In summary: if you make data durable in both FlushFile and SyncFile, then
|
||||
// your users can get safe behavior from mapped files by calling msync(2)
|
||||
// with MS_SYNC, followed by munmap(2), followed by close(2). On Linux, the
|
||||
// msync(2) appears to be optional because close(2) implies dirty page
|
||||
// writeback (cf. http://goo.gl/HyzLTT).
|
||||
//
|
||||
// Because of cases like dup2(2), calls to FlushFile are not necessarily one
|
||||
// to one with calls to OpenFile. They should not be used for reference
|
||||
// counting, and the handle must remain valid even after the method is called
|
||||
// (use ReleaseFileHandle to dispose of it).
|
||||
//
|
||||
// Typical "real" file systems do not implement this, presumably relying on
|
||||
// the kernel to write out the page cache to the block device eventually.
|
||||
// They can get away with this because a later open(2) will see the same
|
||||
// data. A file system that writes to remote storage however probably wants
|
||||
// to at least schedule a real flush, and maybe do it immediately in order to
|
||||
// return any errors that occur.
|
||||
FlushFile(
|
||||
ctx context.Context,
|
||||
req *FlushFileRequest) (*FlushFileResponse, error)
|
||||
|
||||
// Release a previously-minted file handle. The kernel calls this when there
|
||||
// are no more references to an open file: all file descriptors are closed
|
||||
// and all memory mappings are unmapped.
|
||||
//
|
||||
// The kernel guarantees that the handle ID will not be used in further calls
|
||||
// to the file system (unless it is reissued by the file system).
|
||||
ReleaseFileHandle(
|
||||
ctx context.Context,
|
||||
req *ReleaseFileHandleRequest) (*ReleaseFileHandleResponse, error)
|
||||
// Release a previously-minted file handle. The kernel calls this when there
|
||||
// are no more references to an open file: all file descriptors are closed
|
||||
// and all memory mappings are unmapped.
|
||||
//
|
||||
// The kernel guarantees that the handle ID will not be used in further calls
|
||||
// to the file system (unless it is reissued by the file system).
|
||||
type ReleaseFileHandleOp struct {
|
||||
}
|
||||
|
||||
////////////////////////////////////////////////////////////////////////
|
||||
|
|
|
|||
Loading…
Reference in New Issue