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| = 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 them called 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. | + | # Every descriptor is described via struct fdinfo_list_entry (fle). |
− | # Shared file descriptors are distributed between tasks 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. |
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| Example. Restore of connected unix socket by open() method. | | Example. Restore of connected unix socket by open() method. |
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| Note: it's also possible to go to step "2" right after new_fd is written. | | Note: it's also possible to go to step "2" right after new_fd is written. |
| + | |
| + | The peer, which bind() the socket waits in "2", must notify the socket, when it is bound: |
| + | *1)bind(<peer name>); |
| + | *2)set_fds_event(<socket pid>); |
| + | |
| + | = Dependencies = |
| + | # Slave TTY can only be created after respective master peer is restored. But now we wait even more -- till all masters are restored. |
| + | # CTTY must be created after all other TTYs are restored. For all tty dependencies see tty_deps_restored() for the details. |
| + | # Epoll can be created in any time, but it can add a fd in its polling list after the corresponding fle is completely restored. The only exception is a epoll listening other epoll. In this case we wait till listened fle is just created (not restored). See epoll_not_ready_tfd(). |
| + | # Unix socket must wait a peer before connect to it. See peer_is_not_prepared() for the details. |
| + | # TCP sockets have a counter on address use. |
| + | # Implementing a new relationships between fle stages, check, that you are not introducing a circular dependence (with existing). |
| + | |
| + | = Notes = |
| + | # Pipes (and fifos), unix sockets and TTYs generate two fds in their ->open callbacls, the 2nd one can conflict with some other fd the task restores and (!) this "2nd one" may require sending to some other task. |
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| [[Category:Under the hood]] | | [[Category:Under the hood]] |
| [[Category:Files]] | | [[Category:Files]] |