bpf: Add comments to interpret bpf_prog return values
Add a short comment in bpf_iter_run_prog() function to explain how bpf_prog return value is converted to seq_ops->show() return value: bpf_prog return seq_ops()->show() return 0 0 1 -EAGAIN When show() return value is -EAGAIN, the current bpf_seq_read() will end. If the current seq_file buffer is empty, -EAGAIN will return to user space. Otherwise, the buffer will be copied to user space. In both cases, the next bpf_seq_read() call will try to show the same object which returned -EAGAIN previously. Signed-off-by: Yonghong Song <yhs@fb.com> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Andrii Nakryiko <andriin@fb.com> Link: https://lore.kernel.org/bpf/20200513180218.2949517-1-yhs@fb.com
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@ -526,5 +526,11 @@ int bpf_iter_run_prog(struct bpf_prog *prog, void *ctx)
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migrate_enable();
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rcu_read_unlock();
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/* bpf program can only return 0 or 1:
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* 0 : okay
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* 1 : retry the same object
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* The bpf_iter_run_prog() return value
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* will be seq_ops->show() return value.
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*/
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return ret == 0 ? 0 : -EAGAIN;
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}
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