add doc

1 files changed, 217 insertions, 0 deletions

diff --git a/weed/mount/weedfs_file_io.go b/weed/mount/weedfs_file_io.go
new file mode 100644
index 000000000..0a31c3d70
--- /dev/null
+++ b/weed/mount/weedfs_file_io.go
@@ -0,0 +1,217 @@
+package mount
+
+import (
+	"github.com/hanwen/go-fuse/v2/fuse"
+)
+
+/**
+ * Read data
+ *
+ * Read should send exactly the number of bytes requested except
+ * on EOF or error, otherwise the rest of the data will be
+ * substituted with zeroes.  An exception to this is when the file
+ * has been opened in 'direct_io' mode, in which case the return
+ * value of the read system call will reflect the return value of
+ * this operation.
+ *
+ * fi->fh will contain the value set by the open method, or will
+ * be undefined if the open method didn't set any value.
+ *
+ * Valid replies:
+ *   fuse_reply_buf
+ *   fuse_reply_iov
+ *   fuse_reply_data
+ *   fuse_reply_err
+ *
+ * @param req request handle
+ * @param ino the inode number
+ * @param size number of bytes to read
+ * @param off offset to read from
+ * @param fi file information
+ */
+func (wfs *WFS) Read(cancel <-chan struct{}, in *fuse.ReadIn, buf []byte) (fuse.ReadResult, fuse.Status) {
+	return nil, fuse.ENOSYS
+}
+
+/**
+ * Write data
+ *
+ * Write should return exactly the number of bytes requested
+ * except on error.  An exception to this is when the file has
+ * been opened in 'direct_io' mode, in which case the return value
+ * of the write system call will reflect the return value of this
+ * operation.
+ *
+ * Unless FUSE_CAP_HANDLE_KILLPRIV is disabled, this method is
+ * expected to reset the setuid and setgid bits.
+ *
+ * fi->fh will contain the value set by the open method, or will
+ * be undefined if the open method didn't set any value.
+ *
+ * Valid replies:
+ *   fuse_reply_write
+ *   fuse_reply_err
+ *
+ * @param req request handle
+ * @param ino the inode number
+ * @param buf data to write
+ * @param size number of bytes to write
+ * @param off offset to write to
+ * @param fi file information
+ */
+func (wfs *WFS) Write(cancel <-chan struct{}, in *fuse.WriteIn, data []byte) (written uint32, code fuse.Status) {
+	return 0, fuse.ENOSYS
+}
+
+/**
+	 * 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) {
+	return fuse.ENOSYS
+}
+
+/**
+ * Flush method
+ *
+ * This is called on each close() of the opened file.
+ *
+ * Since file descriptors can be duplicated (dup, dup2, fork), for
+ * one open call there may be many flush calls.
+ *
+ * Filesystems shouldn't assume that flush will always be called
+ * after some writes, or that if will be called at all.
+ *
+ * fi->fh will contain the value set by the open method, or will
+ * be undefined if the open method didn't set any value.
+ *
+ * NOTE: the name of the method is misleading, since (unlike
+ * fsync) the filesystem is not forced to flush pending writes.
+ * One reason to flush data is if the filesystem wants to return
+ * write errors during close.  However, such use is non-portable
+ * because POSIX does not require [close] to wait for delayed I/O to
+ * complete.
+ *
+ * If the filesystem supports file locking operations (setlk,
+ * getlk) it should remove all locks belonging to 'fi->owner'.
+ *
+ * If this request is answered with an error code of ENOSYS,
+ * this is treated as success and future calls to flush() will
+ * succeed automatically without being send to the filesystem
+ * process.
+ *
+ * Valid replies:
+ *   fuse_reply_err
+ *
+ * @param req request handle
+ * @param ino the inode number
+ * @param fi file information
+ *
+ * [close]: http://pubs.opengroup.org/onlinepubs/9699919799/functions/close.html
+ */
+func (wfs *WFS) Flush(cancel <-chan struct{}, in *fuse.FlushIn) fuse.Status {
+	return fuse.ENOSYS
+}
+
+/**
+ * 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) {
+}
+
+/**
+ * Synchronize file contents
+ *
+ * If the datasync parameter is non-zero, then only the user data
+ * should be flushed, not the meta data.
+ *
+ * If this request is answered with an error code of ENOSYS,
+ * this is treated as success and future calls to fsync() will
+ * succeed automatically without being send to the filesystem
+ * process.
+ *
+ * Valid replies:
+ *   fuse_reply_err
+ *
+ * @param req request handle
+ * @param ino the inode number
+ * @param datasync flag indicating if only data should be flushed
+ * @param fi file information
+ */
+func (wfs *WFS) Fsync(cancel <-chan struct{}, in *fuse.FsyncIn) (code fuse.Status) {
+	return fuse.ENOSYS
+}