From 90b12bd71bb9fc79a4640b9112c13ef529d0196a Mon Sep 17 00:00:00 2001 From: Laurent Bercot Date: Fri, 5 Dec 2014 22:26:11 +0000 Subject: Initial commit --- doc/fifodir.html | 123 +++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 123 insertions(+) create mode 100644 doc/fifodir.html (limited to 'doc/fifodir.html') diff --git a/doc/fifodir.html b/doc/fifodir.html new file mode 100644 index 0000000..99805ed --- /dev/null +++ b/doc/fifodir.html @@ -0,0 +1,123 @@ + + + + + s6: fifodirs + + + + + + +

+s6
+Software
+skarnet.org +

+ +

Fifodirs

+ +

+ A fifodir is a rendez-vous point between the notifier +of certain events and its listeners. It is implemented via a +directory in the filesystem. No data is stored; it is appropriate to +create fifodirs in a RAM filesystem. +

+ +

Manipulating fifodirs

+ +

C API

+ +

You can create fifodirs via the +ftrigw_fifodir_create() function in +libftrig.
You can send an event to a fifodir via the +ftrigw_notify() function in +libftrig.
You can clean up a fifodir via the +ftrigw_clean() function in +libftrig.
You can destroy fifodirs via the +rm_rf() function in +libstddjb.

+ +

Unix API

+ +

You can create fifodirs with the +s6-mkfifodir command.
You can send an event to a fifodir with the +s6-ftrig-notify command.
You can clean up a fifodir with the +s6-cleanfifodir command.
You can destroy fifodirs with the rm -rf command.

+ +

Internals and Unix permissions

+ +

Notifiers and listeners agree on a fifodir.
The fifodir directory is created by the notifier. It must be writable +by listeners.
To subscribe, a listener atomically creates a named pipe (FIFO) in this +directory and listens to the reading end. This named pipe must be writable +by the notifier.
To send an event to listeners, the notifier writes the event byte to +all the named pipes in the directory. Credit for this idea goes to Stefan +Karrmann.
To unsubscribe, a listener unlinks his named pipe from the directory.

+ +

+Fifodirs are created by, so they always originally have the same uid and gid as, +their notifier. A notifier must be able to make his fifodir either publically +accessible (anyone can subscribe) or restricted (only a given group can +subscribe). +

+ +

+ A publically accessible fifodir must have rights 1733: +

+ +

Anyone can create a fifo in that fifodir
Only the notifier can see all the subscribers' fifos
A listener can only delete its own fifo
A notifier can delete any fifo for cleaning purposes

+ +

+ A restricted fifodir must have the gid g of the group of allowed +listeners and have rights 3730. Unless the notifier is root, it +must be in the group of allowed listeners to be able to create +such a fifodir. +

+ +

Only members of g can create a fifo in that fifodir
Only the notifier can see all the subscribers' fifos
Fifos are always created with gid g
A listener can only delete its own fifo
A notifier can delete any fifo for cleaning purposes

+ +

+ A named pipe in a fifodir must always belong to its listener and have +rights 0622: +

+ +

Only this listener can read on the fifo
Anyone who has reading rights on the fifodir (i.e. only the notifier) +can write to the fifo

+ +

+ The libftrig interface takes care of all +the subtleties. +

+ + + -- cgit v1.2.3