Re: [Xen-devel] [PATCH XEN v8 14/29] tools/libs/foreignmemory: Mention restrictions on fork in docs.

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

On Tue, 2016-01-19 at 13:24 +0000, Wei Liu wrote:
> On Fri, Jan 15, 2016 at 01:22:53PM +0000, Ian Campbell wrote:
> > Signed-off-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
> > ---
> > v6: Also discuss recovering the memory.
> > 
> > v7: Further clarifications regarding forking based on ML discussions.
> > ÂÂÂÂ(Dropped Wei's ack)
> > ---
> > Â.../libs/foreignmemory/include/xenforeignmemory.hÂÂ| 33
> > +++++++++++++++++++++-
> > Â1 file changed, 32 insertions(+), 1 deletion(-)
> > 
> > diff --git a/tools/libs/foreignmemory/include/xenforeignmemory.h
> > b/tools/libs/foreignmemory/include/xenforeignmemory.h
> > index 04ff548..a6d1bdb 100644
> > --- a/tools/libs/foreignmemory/include/xenforeignmemory.h
> > +++ b/tools/libs/foreignmemory/include/xenforeignmemory.h
> > @@ -32,13 +32,44 @@ typedef struct xentoollog_logger xentoollog_logger;
> > Âtypedef struct xenforeignmemory_handle xenforeignmemory_handle;
> > Â
> > Â/*
> > - * Return a handle onto the hypercall driver.ÂÂLogs errors.
> > + * Return a handle onto the foreign memory mapping driver.ÂÂLogs
> > errors.
> > + *
> > + * Note: After fork(2) a child process must not use any opened
> > + * foreignmemory handle inherited from their parent, nor access any
> > + * grant mapped areas associated with that handle.
> > + *
> > + * The child must open a new handle if they want to interact with
> > + * foreignmemory.
> > + *
> > + * Calling exec(2) in a child will safely (and reliably) reclaim any
> > + * resources which were allocated via a xenforeignmemory_handle in the
> > + * parent.
> > + *
> > + * A child which does not call exec(2) may safely call
> > + * xenforeignmemory_close() on a xenforeignmemory_handle inherited
> > + * from their parent. This will attempt to reclaim any resources
> > + * associated with that handle. Note that in some implementations this
> > + * reclamation may not be completely effective, in this case any
> > + * affected resources remain allocated.
> > + *
> > + * Calling xenforeignmemory_close() is the only safe operation on a
> > + * xenforeignmemory_handle which has been inherited.
> > Â */
> > Âxenforeignmemory_handle *xenforeignmemory_open(xentoollog_logger
> > *logger,
> > ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂunsigned open_flags);
> > Â
> > Â/*
> > Â * Close a handle previously allocated with xenforeignmemory_open().
> > + *
> > + * Under normal circumstances (i.e. not in the child after a fork)
> > + * xenforeignmemory_unmap() should be used on all mappings allocated
> 
> "Should" according to RFC 2119 has the connotation of "there might be a
> valid reason to ignore such action". But after reading this passage I
> think we should use "must" here?

RFC 2119 formally defines "SHOULD" not "should" (or "Should"), and in any
case in order to be subject to those formal definitions a document would
need to explicitly reference RFC 2119.

I think most readers of normal English prose would probably take "must" and
"should" to mean mostly the same thing.

If there are other reasons to resend I don't mind switching it to must, but
I don't think it is worth a resend of this mega-series for what is a minor
semantic quibble.

Ian.

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