[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH XEN v8 14/29] tools/libs/foreignmemory: Mention restrictions on fork in docs.
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. > (Dropped Wei's ack) > --- > .../libs/foreignmemory/include/xenforeignmemory.h | 33 > +++++++++++++++++++++- > 1 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; > typedef struct xenforeignmemory_handle xenforeignmemory_handle; > > /* > - * Return a handle onto the hypercall driver. Logs errors. > + * Return a handle onto the foreign memory mapping driver. Logs 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. > */ > xenforeignmemory_handle *xenforeignmemory_open(xentoollog_logger *logger, > unsigned open_flags); > > /* > * 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? Wei. > + * by xenforeignmemory_map() prior to closing the handle in order to > + * free up resources associated with those mappings. > + * > + * This is the only function which may be safely called on a > + * xenforeignmemory_handle in a child after a > + * fork. xenforeignmemory_unmap() must not be called under such > + * circumstances. > */ > int xenforeignmemory_close(xenforeignmemory_handle *fmem); > > -- > 2.1.4 > _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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