[PATCH i-g-t v2] lib/igt_sysfs: make sure to write empty strings

[Lucas De Marchi]

On Wed, Feb 07, 2024 at 05:18:30PM +0100, Kamil Konieczny wrote:
>Hi,
>
>On 2024-02-01 at 14:12:08 +0100, Kamil Konieczny wrote:
>> Hi Lucas,
>> On 2024-01-31 at 19:11:56 -0800, Lucas De Marchi wrote:
>> > 	echo -n "" > /sys/module/<modulename>/parameters/<param>
>> >
>> > doesn't really work as it will just create a open() + close() expecting
>> > the file to be truncated. The same issue happens with igt as it will
>> > stop writing when there are 0 chars to write. Special case the empty
>> > string so it always write a '\0' and make sure igt_sysfs_set() accounts
>> > for the extra null char.
>> >
>> > Shell example:
>> > 	# echo -n "/foo" > /sys/module/firmware_class/parameters/path
>> > 	# cat /sys/module/firmware_class/parameters/path
>> > 	/foo
>> > 	# echo -n "" > /sys/module/firmware_class/parameters/path
>> > 	/foo
>> > 	# # make sure to actually write a \0:
>> > 	echo -ne "\0" > /sys/module/firmware_class/parameters/path
>> > 	# cat /sys/module/firmware_class/parameters/path
>> > 	/foo
>> >
>> > Same thing happens when testing igt_sysfs_set():
>> >        int dirfd = open("/sys/module/firmware_class/parameters", O_RDONLY);
>> >        igt_sysfs_set(dirfd, "path", "");
>> >
>> > Previously it was not really setting the param.
>> >
>> > Signed-off-by: Lucas De Marchi <lucas.demarchi at intel.com>
>> > ---
>> >  lib/igt_sysfs.c | 12 ++++++++++--
>> >  1 file changed, 10 insertions(+), 2 deletions(-)
>> >
>> > diff --git a/lib/igt_sysfs.c b/lib/igt_sysfs.c
>> > index 567b4f6d5..64c2aaabb 100644
>> > --- a/lib/igt_sysfs.c
>> > +++ b/lib/igt_sysfs.c
>> > @@ -406,7 +406,7 @@ int igt_sysfs_read(int dir, const char *attr, void *data, int len)
>> >   */
>> >  bool igt_sysfs_set(int dir, const char *attr, const char *value)
>> >  {
>> > -	int len = strlen(value);
>> > +	int len = strlen(value) + 1;
>> >  	return igt_sysfs_write(dir, attr, value, len) == len;
>>
>> Why not adding write "\n" at end?
>
>So what about changing this only for zero?
>
>if (!len)
>        ++len;

ok

Lucas De Marchi