seaweedfs/weed/mount/weedfs_file_io.go

package mount

import (
	"github.com/hanwen/go-fuse/v2/fuse"
)

/**
	 * Open a file
	 *
	 * Open flags are available in fi->flags. The following rules
	 * apply.
	 *
	 *  - Creation (O_CREAT, O_EXCL, O_NOCTTY) flags will be
	 *    filtered out / handled by the kernel.
	 *
	 *  - Access modes (O_RDONLY, O_WRONLY, O_RDWR) should be used
	 *    by the filesystem to check if the operation is
	 *    permitted.  If the ``-o default_permissions`` mount
	 *    option is given, this check is already done by the
	 *    kernel before calling open() and may thus be omitted by
	 *    the filesystem.
	 *
	 *  - When writeback caching is enabled, the kernel may send
	 *    read requests even for files opened with O_WRONLY. The
	 *    filesystem should be prepared to handle this.
	 *
	 *  - When writeback caching is disabled, the filesystem is
	 *    expected to properly handle the O_APPEND flag and ensure
	 *    that each write is appending to the end of the file.
	 *
         *  - When writeback caching is enabled, the kernel will
	 *    handle O_APPEND. However, unless all changes to the file
	 *    come through the kernel this will not work reliably. The
	 *    filesystem should thus either ignore the O_APPEND flag
	 *    (and let the kernel handle it), or return an error
	 *    (indicating that reliably O_APPEND is not available).
	 *
	 * Filesystem may store an arbitrary file handle (pointer,
	 * index, etc) in fi->fh, and use this in other all other file
	 * operations (read, write, flush, release, fsync).
	 *
	 * Filesystem may also implement stateless file I/O and not store
	 * anything in fi->fh.
	 *
	 * There are also some flags (direct_io, keep_cache) which the
	 * filesystem may set in fi, to change the way the file is opened.
	 * See fuse_file_info structure in <fuse_common.h> for more details.
	 *
	 * If this request is answered with an error code of ENOSYS
	 * and FUSE_CAP_NO_OPEN_SUPPORT is set in
	 * `fuse_conn_info.capable`, this is treated as success and
	 * future calls to open and release will also succeed without being
	 * sent to the filesystem process.
	 *
	 * Valid replies:
	 *   fuse_reply_open
	 *   fuse_reply_err
	 *
	 * @param req request handle
	 * @param ino the inode number
	 * @param fi file information
*/
func (wfs *WFS) Open(cancel <-chan struct{}, in *fuse.OpenIn, out *fuse.OpenOut) (status fuse.Status) {
	fileHandle, code := wfs.AcquireHandle(in.NodeId, in.Uid, in.Gid)
	if code == fuse.OK {
		out.Fh = uint64(fileHandle.fh)
		// TODO https://github.com/libfuse/libfuse/blob/master/include/fuse_common.h#L64
	}
	return code
}

/**
 * Release an open file
 *
 * Release is called when there are no more references to an open
 * file: all file descriptors are closed and all memory mappings
 * are unmapped.
 *
 * For every open call there will be exactly one release call (unless
 * the filesystem is force-unmounted).
 *
 * The filesystem may reply with an error, but error values are
 * not returned to close() or munmap() which triggered the
 * release.
 *
 * fi->fh will contain the value set by the open method, or will
 * be undefined if the open method didn't set any value.
 * fi->flags will contain the same flags as for open.
 *
 * Valid replies:
 *   fuse_reply_err
 *
 * @param req request handle
 * @param ino the inode number
 * @param fi file information
 */
func (wfs *WFS) Release(cancel <-chan struct{}, in *fuse.ReleaseIn) {
	wfs.ReleaseHandle(FileHandleId(in.Fh))
}