string: drop __must_check from strscpy() and restore strscpy() usages in cgroup
BugLink: https://bugs.launchpad.net/bugs/1818813 commit 08a77676 upstream. e7fd37ba ("cgroup: avoid copying strings longer than the buffers") converted possibly unsafe strncpy() usages in cgroup to strscpy(). However, although the callsites are completely fine with truncated copied, because strscpy() is marked __must_check, it led to the following warnings. kernel/cgroup/cgroup.c: In function ‘cgroup_file_name’: kernel/cgroup/cgroup.c:1400:10: warning: ignoring return value of ‘strscpy’, declared with attribute warn_unused_result [-Wunused-result] strscpy(buf, cft->name, CGROUP_FILE_NAME_MAX); ^ To avoid the warnings, 50034ed4 ("cgroup: use strlcpy() instead of strscpy() to avoid spurious warning") switched them to strlcpy(). strlcpy() is worse than strlcpy() because it unconditionally runs strlen() on the source string, and the only reason we switched to strlcpy() here was because it was lacking __must_check, which doesn't reflect any material differences between the two function. It's just that someone added __must_check to strscpy() and not to strlcpy(). These basic string copy operations are used in variety of ways, and one of not-so-uncommon use cases is safely handling truncated copies, where the caller naturally doesn't care about the return value. The __must_check doesn't match the actual use cases and forces users to opt for inferior variants which lack __must_check by happenstance or spread ugly (void) casts. Remove __must_check from strscpy() and restore strscpy() usages in cgroup. Signed-off-by: Tejun Heo <tj@kernel.org> Suggested-by: Linus Torvalds <torvalds@linux-foundation.org> Cc: Ma Shimiao <mashimiao.fnst@cn.fujitsu.com> Cc: Arnd Bergmann <arnd@arndb.de> Cc: Chris Metcalf <cmetcalf@ezchip.com> [backport only the string.h portion to remove build warnings starting to show up - gregkh] Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Signed-off-by: Juerg Haefliger <juergh@canonical.com> Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>
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