Added notes about the page cache.

Aaron Jacobs 2015-03-05 20:25:40 +11:00
parent 4e169a0602
commit a612b8b8d6
1 changed files with 29 additions and 0 deletions

View File

@ -151,11 +151,40 @@ type FileSystem interface {
req *OpenFileRequest) (*OpenFileResponse, error)
// Read data from a file previously opened with CreateFile or OpenFile.
// Note that this method is not called for every call to read(2) by the end
// user; some reads may be served by the page cache. See notes on Write for
// more.
ctx context.Context,
req *ReadFileRequest) (*ReadFileResponse, error)
// Write data to a file previously opened with CreateFile or OpenFile.
// When the user writes data using write(2), the write goes into the page
// cache and the page is marked dirty. Later the kernel may write back the
// page via the FUSE VFS layer, causing this method to be called:
// * The kernel calls address_space_operations::writepage when a dirty page
// needs to be written to backing store (see vfs.txt). Fuse sets this to
// fuse_writepage (see file.c).
// * fuse_writepage calls fuse_writepage_locked.
// * fuse_writepage_locked makes a write request to the userspace server.
// Note that writes *will* be received before a call to Flush when closing
// the file descriptor to which they were written:
// * fuse_flush calls write_inode_now, which appears to start a writeback
// in the background (it talks about a "flusher thread").
// * fuse_flush then calls fuse_sync_writes, which "[waits] for all pending
// writepages on the inode to finish".
// * Only then does fuse_flush finally send the flush request.
// TODO(jacobsa): Add links for all of the references above.
ctx context.Context,
req *WriteFileRequest) (*WriteFileResponse, error)