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ethtool: Clarify len/n_stats fields in/out semantics

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Document that the 'len' field in ethtool_gstrings and 'n_stats' field in
ethtool_stats optionally serve dual purposes: on entry they specify the
number of items requested, and on return they indicate the number
actually returned (which is not necessarily the same).

Signed-off-by: Gal Pressman <gal@nvidia.com>
Reviewed-by: Dragos Tatulea <dtatulea@nvidia.com>
Link: https://patch.msgid.link/20260115060544.481550-1-gal@nvidia.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Gal Pressman 2026-01-15 08:05:44 +02:00 committed by Jakub Kicinski
parent c27022497d
commit 567873005d
1 changed files with 16 additions and 2 deletions
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18
include/uapi/linux/ethtool.h
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@ -1096,13 +1096,20 @@ enum ethtool_module_fw_flash_status {
* struct ethtool_gstrings - string set for data tagging
* @cmd: Command number = %ETHTOOL_GSTRINGS
* @string_set: String set ID; one of &enum ethtool_stringset
* @len: On return, the number of strings in the string set
* @len: Number of strings in the string set
* @data: Buffer for strings. Each string is null-padded to a size of
* %ETH_GSTRING_LEN.
*
* Users must use %ETHTOOL_GSSET_INFO to find the number of strings in
* the string set. They must allocate a buffer of the appropriate
* size immediately following this structure.
*
* Setting @len on input is optional (though preferred), but must be zeroed
* otherwise.
* When set, @len will return the requested count if it matches the actual
* count; otherwise, it will be zero.
* This prevents issues when the number of strings is different than the
* userspace allocation.
*/
struct ethtool_gstrings {
__u32 cmd;
@ -1179,13 +1186,20 @@ struct ethtool_test {
/**
* struct ethtool_stats - device-specific statistics
* @cmd: Command number = %ETHTOOL_GSTATS
* @n_stats: On return, the number of statistics
* @n_stats: Number of statistics
* @data: Array of statistics
*
* Users must use %ETHTOOL_GSSET_INFO or %ETHTOOL_GDRVINFO to find the
* number of statistics that will be returned. They must allocate a
* buffer of the appropriate size (8 * number of statistics)
* immediately following this structure.
*
* Setting @n_stats on input is optional (though preferred), but must be zeroed
* otherwise.
* When set, @n_stats will return the requested count if it matches the actual
* count; otherwise, it will be zero.
* This prevents issues when the number of stats is different than the
* userspace allocation.
*/
struct ethtool_stats {
__u32 cmd;