27 lines
942 B
Markdown
27 lines
942 B
Markdown
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# Extend
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The extend mechanism allows a structure to be extended by a model. It works by
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placing an array of pointers indexed by the model identifier (char) inside the
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structure. Most of the structures of the emulator have a `ext` member, allowing
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them to be extended.
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Models are forbidden to access information from other models than their own.
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The function `void extend_set(struct extend *ext, int id, void *ctx)` stores the
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ctx pointer inside the extend structure for the model with the given id.
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Use `void *extend_get(struct extend *ext, int id)` to retrieve its value.
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A helper macro `EXT(st, m)` directly attempts to find the member `ext` in the
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structure st, and return the pointer of the model `m`.
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Here is an example where Nanos6 stores its own CPU information:
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struct cpu *syscpu;
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struct nanos6_cpu *cpu;
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extend_set(&syscpu->ext, '6', cpu);
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cpu = extend_get(&syscpu->ext, '6');
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cpu = EXT(syscpu, '6'); /* same */
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