[PATCH bpf-next] bpf: Clarify return value of probe str helpers

[PATCH bpf-next] bpf: Clarify return value of probe str helpers

[Brendan Jackman]

When the buffer is too small to contain the input string, these
helpers return the length of the buffer, not the length of the
original string. This tries to make the docs totally clear about
that, since "the length of the [copied ]string" could also refer to
the length of the input.

Signed-off-by: Brendan Jackman <jackmanb@google.com>
---
 include/uapi/linux/bpf.h       | 10 +++++-----
 tools/include/uapi/linux/bpf.h | 10 +++++-----
 2 files changed, 10 insertions(+), 10 deletions(-)

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 77d7c1bb2923..a1ad32456f89 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -2993,10 +2993,10 @@ union bpf_attr {
  * 		string length is larger than *size*, just *size*-1 bytes are
  * 		copied and the last byte is set to NUL.
  *
- * 		On success, the length of the copied string is returned. This
- * 		makes this helper useful in tracing programs for reading
- * 		strings, and more importantly to get its length at runtime. See
- * 		the following snippet:
+ * 		On success, returns the number of bytes that were written,
+ * 		including the terminal NUL. This makes this helper useful in
+ * 		tracing programs for reading strings, and more importantly to
+ * 		get its length at runtime. See the following snippet:
  *
  * 		::
  *
@@ -3024,7 +3024,7 @@ union bpf_attr {
  * 		**->mm->env_start**: using this helper and the return value,
  * 		one can quickly iterate at the right offset of the memory area.
  * 	Return
- * 		On success, the strictly positive length of the string,
+ * 		On success, the strictly positive length of the output string,
  * 		including the trailing NUL character. On error, a negative
  * 		value.
  *
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index 77d7c1bb2923..a1ad32456f89 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -2993,10 +2993,10 @@ union bpf_attr {
  * 		string length is larger than *size*, just *size*-1 bytes are
  * 		copied and the last byte is set to NUL.
  *
- * 		On success, the length of the copied string is returned. This
- * 		makes this helper useful in tracing programs for reading
- * 		strings, and more importantly to get its length at runtime. See
- * 		the following snippet:
+ * 		On success, returns the number of bytes that were written,
+ * 		including the terminal NUL. This makes this helper useful in
+ * 		tracing programs for reading strings, and more importantly to
+ * 		get its length at runtime. See the following snippet:
  *
  * 		::
  *
@@ -3024,7 +3024,7 @@ union bpf_attr {
  * 		**->mm->env_start**: using this helper and the return value,
  * 		one can quickly iterate at the right offset of the memory area.
  * 	Return
- * 		On success, the strictly positive length of the string,
+ * 		On success, the strictly positive length of the output string,
  * 		including the trailing NUL character. On error, a negative
  * 		value.
  *

base-commit: e22d7f05e445165e58feddb4e40cc9c0f94453bc
--
2.30.0.284.gd98b1dd5eaa7-goog

Re: [PATCH bpf-next] bpf: Clarify return value of probe str helpers

[KP Singh]

On Tue, Jan 12, 2021 at 1:34 PM Brendan Jackman <jackmanb@google.com> wrote:
>
> When the buffer is too small to contain the input string, these
> helpers return the length of the buffer, not the length of the
> original string. This tries to make the docs totally clear about
> that, since "the length of the [copied ]string" could also refer to
> the length of the input.
>
> Signed-off-by: Brendan Jackman <jackmanb@google.com>

Acked-by: KP Singh <kpsingh@kernel.org>

Re: [PATCH bpf-next] bpf: Clarify return value of probe str helpers

[Yonghong Song]

On 1/12/21 4:34 AM, Brendan Jackman wrote:
> When the buffer is too small to contain the input string, these
> helpers return the length of the buffer, not the length of the
> original string. This tries to make the docs totally clear about
> that, since "the length of the [copied ]string" could also refer to
> the length of the input.
> 
> Signed-off-by: Brendan Jackman <jackmanb@google.com>

Acked-by: Yonghong Song <yhs@fb.com>

Re: [PATCH bpf-next] bpf: Clarify return value of probe str helpers

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to bpf/bpf-next.git (refs/heads/master):

On Tue, 12 Jan 2021 12:34:22 +0000 you wrote:
> When the buffer is too small to contain the input string, these
> helpers return the length of the buffer, not the length of the
> original string. This tries to make the docs totally clear about
> that, since "the length of the [copied ]string" could also refer to
> the length of the input.
> 
> Signed-off-by: Brendan Jackman <jackmanb@google.com>
> 
> [...]

Here is the summary with links:
  - [bpf-next] bpf: Clarify return value of probe str helpers
    https://git.kernel.org/bpf/bpf-next/c/c6458e72f6fd

You are awesome, thank you!
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