Re: [libvirt] [PATCH v7 2/6] qapi: Introduce add-fd, remove-fd, query-fdsets

On 08/07/2012 09:58 AM, Corey Bryant wrote: > This patch adds support that enables passing of file descriptors > to the QEMU monitor where they will be stored in specified file > descriptor sets. > > A file descriptor set can be used by a client like libvirt to > store file descriptors for the same file. This allows the > client to open a file with different access modes (O_RDWR, > O_WRONLY, O_RDONLY) and add/remove the passed fds to/from an fd > set as needed. This will allow QEMU to (in a later patch in this > series) "open" and "reopen" the same file by dup()ing the fd in > the fd set that corresponds to the file, where the fd has the > matching access mode flag that QEMU requests. > > The new QMP commands are: > add-fd: Add a file descriptor to an fd set > remove-fd: Remove a file descriptor from an fd set > query-fdsets: Return information describing all fd sets > > + > +# @AddfdInfo: > +# > +# Information about a file descriptor that was added to an fd set. > +# > +# @fdset_id: The ID of the fd set that @fd was added to. > +# > +# @fd: The file descriptor that was received via SCM rights and > +# added to the fd set. > +# > +# Since: 1.2.0 We're not very consistent on '1.2' vs. '1.2.0' in since listings, but that's probably worth a global cleanup closer to hard freeze. > +## > +{ 'type': 'AddfdInfo', 'data': {'fdset_id': 'int', 'fd': 'int'} } This is a new command, so s/fdset_id/fdset-id/ > + > +## > +# @add-fd: > +# > +# Add a file descriptor, that was passed via SCM rights, to an fd set. > +# > +# @fdset_id: #optional The ID of the fd set to add the file descriptor to. > +# > +# Returns: @AddfdInfo on success > +# If file descriptor was not received, FdNotSupplied > +# If @fdset_id does not exist, FdSetNotFound > +# > +# Notes: The list of fd sets is shared by all monitor connections. > +# > +# If @fdset_id is not specified, a new fd set will be created. > +# > +# Since: 1.2.0 > +## > +{ 'command': 'add-fd', 'data': {'*fdset_id': 'int'}, Again, s/fdset_id/fdset-id/ > + 'returns': 'AddfdInfo' } > + > +## > +# @remove-fd: > +# > +# Remove a file descriptor from an fd set. > +# > +# @fdset_id: The ID of the fd set that the file descriptor belongs to. > +# > +# @fd: #optional The file descriptor that is to be removed. > +# > +# Returns: Nothing on success > +# If @fdset_id or @fd is not found, FdNotFound > +# > +# Since: 1.2.0 > +# > +# Notes: The list of fd sets is shared by all monitor connections. > +# > +# File descriptors that are removed: > +# o will not be closed until the reference count corresponding > +# to @fdset_id reaches zero. > +# o will not be available for use after successful completion > +# of the remove-fd command. > +# > +# If @fd is not specified, all file descriptors in @fdset_id > +# will be removed. > +## > +{ 'command': 'remove-fd', 'data': {'fdset_id': 'int', '*fd': 'int'} } And again. > + > +## > +# @FdsetFdInfo: > +# > +# Information about a file descriptor that belongs to an fd set. > +# > +# @fd: The file descriptor value. > +# > +# @removed: If true, the remove-fd command has been issued for this fd. > +# > +# Since: 1.2.0 > +## > +{ 'type': 'FdsetFdInfo', 'data': {'fd': 'int', 'removed': 'bool'} } Is it worth providing any additional information? For example, knowing whether the fd is O_RDONLY, O_WRONLY, or O_RDWR might be beneficial to management apps trying to discover what fds are already present after a reconnection, in order to decide whether to close them without having to resort to /proc/$qemupid/fdinfo/nnn lookups. It might even be worth marking such information optional, present only when 'removed':false.