Changes

= Masters and slaves =

= Masters and slaves =

# A file may be referred by several file descriptors. The descriptors may belong to a single process or to several processes.

# A file may be referred to by several file descriptors. The descriptors may belong to a single process or to several processes.

# Group of descriptors referring to the same file is called shared. One of the descriptors is named master, others are slaves.

# A group of descriptors referring to the same file is called shared. One of the descriptors is named master, others are slaves.

# Every descriptor is discribed via struct fdinfo_list_entry (fle).

# Every descriptor is described via struct fdinfo_list_entry (fle).

# One process opens a master fle of a file, while other processes, sharing the file, obtain it using scm_rights. See send_fds() and receive_fds() for the details.

# One process opens a master fle of a file, while other processes, sharing the file, obtain it using scm_rights. See send_fds() and receive_fds() for details.

= Per-process files restore =

= Per-process file restore =

Every file types is described via structure file_desc. We sequentially call file_desc::ops::open(struct file_desc *d, int *new_fd) method for every master file of a process until all masters are restored. The open methods may return three values:

Every file type is described via structure file_desc. We sequentially call file_desc::ops::open(struct file_desc *d, int *new_fd) method for every master file of a process until all masters are restored. The open methods may return three values:

*  0  -- restore of the master file is successefuly finished;

*  0  -- restore of the master file is successefuly finished;

*  1  -- restore is in progress or it can't be started yet, because of it depends on another files, so the method should be called once again;

*  1  -- restore is in progress or it can't be started yet, because of it depends on another files, so the method should be called once again;

* -1 -- restore failed.

* -1 -- restore failed.

Right after a file is open at first time, the open method must return fd value in new_fd argument. This allows the common code to send this master to other processes to reopen the master as a slave as soon as possible. The same time, returning of not-negative new_fd does not mean, that the master is restored. The open() callback may return not-negative new_fd and "1" as return value at the same time.

Right after a file is opened for the first time, the open method must return the fd value in the new_fd argument. This allows the common code to send this master to other processes to reopen the master as a slave as soon as possible. At the same time, returning a non-negative new_fd does not mean that the master is restored. The open() callback may return a non-negative new_fd and "1" as return value at the same time.

Example. Restore of connected unix socket by open() method.

Example. Restore of connected unix socket by open() method.