[PATCH net-next] tools: ynl: rework the string representation of NlError

[PATCH net-next] tools: ynl: rework the string representation of NlError

[Jakub Kicinski]

In early days of YNL development dumping the NlMsg on errors
was quite useful, as the library itself could have been buggy.
These days increasingly the NlMsg is just taking up screen space
and means nothing to a typical user. Try to format the errors
more in line with how YNL C formats its errors strings.

Before:
  $ ynl --family ethtool  --do channels-set  --json '{}'
  Netlink error: Invalid argument
  nl_len = 44 (28) nl_flags = 0x300 nl_type = 2
	error: -22
	extack: {'miss-type': 'header'}

  $ ynl --family ethtool  --do channels-set  --json '{..., "tx-count": 999}'
  Netlink error: Invalid argument
  nl_len = 88 (72) nl_flags = 0x300 nl_type = 2
	error: -22
	extack: {'msg': 'requested channel count exceeds maximum', 'bad-attr': '.tx-count'}

After:
  $ ynl --family ethtool  --do channels-set  --json '{}'
  Netlink error: Invalid argument {'miss-type': 'header'}

  $ ynl --family ethtool  --do channels-set  --json '{..., "tx-count": 999}'
  Netlink error: requested channel count exceeds maximum: Invalid argument {'bad-attr': '.tx-count'}

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
---
CC: donald.hunter@gmail.com
CC: ast@fiberby.net
---
 tools/net/ynl/pyynl/lib/ynl.py | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/tools/net/ynl/pyynl/lib/ynl.py b/tools/net/ynl/pyynl/lib/ynl.py
index 62383c70ebb9..bac9eb33ba89 100644
--- a/tools/net/ynl/pyynl/lib/ynl.py
+++ b/tools/net/ynl/pyynl/lib/ynl.py
@@ -105,7 +105,17 @@ from .nlspec import SpecFamily
     self.error = -nl_msg.error
 
   def __str__(self):
-    return f"Netlink error: {os.strerror(self.error)}\n{self.nl_msg}"
+    msg = "Netlink error: "
+
+    extack = self.nl_msg.extack.copy() if self.nl_msg.extack else {}
+    if extack:
+        if 'msg' in extack:
+            msg += extack['msg'] + ': '
+            del extack['msg']
+    msg += os.strerror(self.error)
+    if extack:
+        msg += ' ' + str(extack)
+    return msg
 
 
 class ConfigError(Exception):
-- 
2.51.0

Re: [PATCH net-next] tools: ynl: rework the string representation of NlError

[Donald Hunter]

Jakub Kicinski <kuba@kernel.org> writes:

> In early days of YNL development dumping the NlMsg on errors
> was quite useful, as the library itself could have been buggy.
> These days increasingly the NlMsg is just taking up screen space
> and means nothing to a typical user. Try to format the errors
> more in line with how YNL C formats its errors strings.
>
> Before:
>   $ ynl --family ethtool  --do channels-set  --json '{}'
>   Netlink error: Invalid argument
>   nl_len = 44 (28) nl_flags = 0x300 nl_type = 2
> 	error: -22
> 	extack: {'miss-type': 'header'}
>
>   $ ynl --family ethtool  --do channels-set  --json '{..., "tx-count": 999}'
>   Netlink error: Invalid argument
>   nl_len = 88 (72) nl_flags = 0x300 nl_type = 2
> 	error: -22
> 	extack: {'msg': 'requested channel count exceeds maximum', 'bad-attr': '.tx-count'}
>
> After:
>   $ ynl --family ethtool  --do channels-set  --json '{}'
>   Netlink error: Invalid argument {'miss-type': 'header'}
>
>   $ ynl --family ethtool  --do channels-set  --json '{..., "tx-count": 999}'
>   Netlink error: requested channel count exceeds maximum: Invalid argument {'bad-attr': '.tx-count'}
>
> Signed-off-by: Jakub Kicinski <kuba@kernel.org>
> ---
> CC: donald.hunter@gmail.com
> CC: ast@fiberby.net
> ---
>  tools/net/ynl/pyynl/lib/ynl.py | 12 +++++++++++-
>  1 file changed, 11 insertions(+), 1 deletion(-)
>
> diff --git a/tools/net/ynl/pyynl/lib/ynl.py b/tools/net/ynl/pyynl/lib/ynl.py
> index 62383c70ebb9..bac9eb33ba89 100644
> --- a/tools/net/ynl/pyynl/lib/ynl.py
> +++ b/tools/net/ynl/pyynl/lib/ynl.py
> @@ -105,7 +105,17 @@ from .nlspec import SpecFamily
>      self.error = -nl_msg.error
>  
>    def __str__(self):
> -    return f"Netlink error: {os.strerror(self.error)}\n{self.nl_msg}"
> +    msg = "Netlink error: "
> +
> +    extack = self.nl_msg.extack.copy() if self.nl_msg.extack else {}
> +    if extack:

The 'if extack' condition seems redundant given the way extack is
initialised.

Otherwise LGTM.

> +        if 'msg' in extack:
> +            msg += extack['msg'] + ': '
> +            del extack['msg']
> +    msg += os.strerror(self.error)
> +    if extack:
> +        msg += ' ' + str(extack)
> +    return msg
>  
>  
>  class ConfigError(Exception):