Commit 2e3ed68b authored May 13, 2020 by Yonghong Song Committed by Alexei Starovoitov May 13, 2020

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

parent 21aef70e

kernel/bpf/bpf_iter.c

+6 −0

Original line number	Diff line number	Diff line
		@@ -526,5 +526,11 @@ int bpf_iter_run_prog(struct bpf_prog prog, void ctx)
		migrate_enable();
		rcu_read_unlock();

		/* bpf program can only return 0 or 1:
		* 0 : okay
		* 1 : retry the same object
		* The bpf_iter_run_prog() return value
		* will be seq_ops->show() return value.
		*/
		return ret == 0 ? 0 : -EAGAIN;
		}

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