[PATCH AUTOSEL 4.19 094/146] UAPI: ndctl: Fix g++-unsupported initialisation in headers

Sasha Levin
2018-10-31T23:07:12Z

From: David Howells <dhowells@redhat.com>

[ Upstream commit 9607871f37dc3e717639694b8d0dc738f2a68efc ]

The following code in the linux/ndctl header file:

static inline const char *nvdimm_bus_cmd_name(unsigned cmd)
{
static const char * const names[] = {
[ND_CMD_ARS_CAP] = "ars_cap",
[ND_CMD_ARS_START] = "ars_start",
[ND_CMD_ARS_STATUS] = "ars_status",
[ND_CMD_CLEAR_ERROR] = "clear_error",
[ND_CMD_CALL] = "cmd_call",
};

if (cmd < ARRAY_SIZE(names) && names[cmd])
return names[cmd];
return "unknown";
}

is broken in a number of ways:

(1) ARRAY_SIZE() is not generally defined.

(2) g++ does not support "non-trivial" array initialisers fully yet.

(3) Every file that calls this function will acquire a copy of names[].

The same goes for nvdimm_cmd_name().

Fix all three by converting to a switch statement where each case returns a
string. That way if cmd is a constant, the compiler can trivially reduce it
and, if not, the compiler can use a shared lookup table if it thinks that is
more efficient.

A better way would be to remove these functions and their arrays from the
header entirely.

Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
include/uapi/linux/ndctl.h | 48 +++++++++++++++++---------------------
1 file changed, 21 insertions(+), 27 deletions(-)

diff --git a/include/uapi/linux/ndctl.h b/include/uapi/linux/ndctl.h
index 7e27070b9440..2f2c43d633c5 100644
--- a/include/uapi/linux/ndctl.h
+++ b/include/uapi/linux/ndctl.h
@@ -128,37 +128,31 @@ enum {

static inline const char *nvdimm_bus_cmd_name(unsigned cmd)
{
- static const char * const names[] = {
- [ND_CMD_ARS_CAP] = "ars_cap",
- [ND_CMD_ARS_START] = "ars_start",
- [ND_CMD_ARS_STATUS] = "ars_status",
- [ND_CMD_CLEAR_ERROR] = "clear_error",
- [ND_CMD_CALL] = "cmd_call",
- };
-
- if (cmd < ARRAY_SIZE(names) && names[cmd])
- return names[cmd];
- return "unknown";
+ switch (cmd) {
+ case ND_CMD_ARS_CAP: return "ars_cap";
+ case ND_CMD_ARS_START: return "ars_start";
+ case ND_CMD_ARS_STATUS: return "ars_status";
+ case ND_CMD_CLEAR_ERROR: return "clear_error";
+ case ND_CMD_CALL: return "cmd_call";
+ default: return "unknown";
+ }
}

static inline const char *nvdimm_cmd_name(unsigned cmd)
{
- static const char * const names[] = {
- [ND_CMD_SMART] = "smart",
- [ND_CMD_SMART_THRESHOLD] = "smart_thresh",
- [ND_CMD_DIMM_FLAGS] = "flags",
- [ND_CMD_GET_CONFIG_SIZE] = "get_size",
- [ND_CMD_GET_CONFIG_DATA] = "get_data",
- [ND_CMD_SET_CONFIG_DATA] = "set_data",
- [ND_CMD_VENDOR_EFFECT_LOG_SIZE] = "effect_size",
- [ND_CMD_VENDOR_EFFECT_LOG] = "effect_log",
- [ND_CMD_VENDOR] = "vendor",
- [ND_CMD_CALL] = "cmd_call",
- };
-
- if (cmd < ARRAY_SIZE(names) && names[cmd])
- return names[cmd];
- return "unknown";
+ switch (cmd) {
+ case ND_CMD_SMART: return "smart";
+ case ND_CMD_SMART_THRESHOLD: return "smart_thresh";
+ case ND_CMD_DIMM_FLAGS: return "flags";
+ case ND_CMD_GET_CONFIG_SIZE: return "get_size";
+ case ND_CMD_GET_CONFIG_DATA: return "get_data";
+ case ND_CMD_SET_CONFIG_DATA: return "set_data";
+ case ND_CMD_VENDOR_EFFECT_LOG_SIZE: return "effect_size";
+ case ND_CMD_VENDOR_EFFECT_LOG: return "effect_log";
+ case ND_CMD_VENDOR: return "vendor";
+ case ND_CMD_CALL: return "cmd_call";
+ default: return "unknown";
+ }
}

#define ND_IOCTL 'N'
--
2.17.1