Messages in this thread | | | Date | Tue, 4 Nov 2014 15:14:55 -0800 | Subject | Re: [PATCH net-next 3/7] bpf: add array type of eBPF maps | From | Alexei Starovoitov <> |
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On Tue, Nov 4, 2014 at 1:58 AM, Daniel Borkmann <dborkman@redhat.com> wrote: >> + >> + memcpy(array->value + array->elem_size * index, value, >> array->elem_size); > > What would protect this from concurrent updates?
nothing. that's what I meant in commit log: - map_update_elem() replaces elements in an non-atomic way (for atomic updates hashtable type should be used instead)
The array map is like C array of structures. Nothing protects concurrent access. It's used in the cases where accuracy is not needed or when there is no concurrent access. To compute a histogram of events in tracing the array of integers is used. Every integer is a counter. Program increments it (may be without using xadd) and user space periodically reads it back. map_update_elem() is called by userspace once to initialize it if zero-init is not enough. Programs do lookup() and modify the values. For array type update() method is used rarely, delete() is never used and get_next() is needed for completeness to browse maps through common map API. I'm guessing you're asking, because it may feel that adding a lock() will help to make it more useful? ;) It's not, since programs cannot take a lock().
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