Re: [ndctl PATCH v2] cxl/list: remove libtracefs build dependency for --media-errors

[<dan.j.williams@intel.com>]

Alison Schofield wrote:
> When the --media-errors option was added to cxl list it inadvertently
> changed the optional libtracefs requirement into a mandatory one.
> Ndctl versions 80,81,82 no longer build without libtracefs.
> 
> Remove that dependency.
> 
> When libtracefs is disabled the user will see a 'Notice' level
> message, like this:
> 	$ cxl list -r region0 --media-errors --targets
> 	cxl list: cmd_list: --media-errors support disabled at build time
> 
> ...followed by the region listing including the output for any other
> valid command line options, like --targets in the example above.
> 
> When libtracefs is disabled the cxl-poison.sh unit test is omitted.
> 
> The man page gets a note:
> 	The media-error option is only available with -Dlibtracefs=enabled.
> 
> Reported-by: Andreas Hasenack <andreas.hasenack@canonical.com>
> Fixes: d7532bb049e0 ("cxl/list: add --media-errors option to cxl list")
> Closes: https://github.com/pmem/ndctl/issues/289
> Signed-off-by: Alison Schofield <alison.schofield@intel.com>
> ---
> 
> Changes in v2:
> - Notify and continue when --media-error info is unavailable (Dan)
> 
> 
>  Documentation/cxl/cxl-list.txt |  2 ++
>  config.h.meson                 |  2 +-
>  cxl/json.c                     | 15 ++++++++++++++-
>  cxl/list.c                     |  6 ++++++
>  test/meson.build               |  9 +++++++--
>  5 files changed, 30 insertions(+), 4 deletions(-)
> 
> diff --git a/Documentation/cxl/cxl-list.txt b/Documentation/cxl/cxl-list.txt
> index 9a9911e7dd9b..0595638ee054 100644
> --- a/Documentation/cxl/cxl-list.txt
> +++ b/Documentation/cxl/cxl-list.txt
> @@ -425,6 +425,8 @@ OPTIONS
>  	"source:" is one of: External, Internal, Injected, Vendor Specific,
>  	or Unknown, as defined in CXL Specification v3.1 Table 8-140.
>  
> +The media-errors option is only available with '-Dlibtracefs=enabled'.
> +
>  ----
>  # cxl list -m mem9 --media-errors -u
>  {
> diff --git a/config.h.meson b/config.h.meson
> index f75db3e6360f..e8539f8d04df 100644
> --- a/config.h.meson
> +++ b/config.h.meson
> @@ -19,7 +19,7 @@
>  /* ndctl test support */
>  #mesondefine ENABLE_TEST
>  
> -/* cxl monitor support */
> +/* cxl monitor and cxl list --media-errors support */
>  #mesondefine ENABLE_LIBTRACEFS
>  
>  /* Define to 1 if big-endian-arch */
> diff --git a/cxl/json.c b/cxl/json.c
> index e65bd803b706..a75928bf43ed 100644
> --- a/cxl/json.c
> +++ b/cxl/json.c
> @@ -9,12 +9,15 @@
>  #include <json-c/json.h>
>  #include <json-c/printbuf.h>
>  #include <ccan/short_types/short_types.h>
> +
> +#ifdef ENABLE_LIBTRACEFS
>  #include <tracefs.h>
> +#include "../util/event_trace.h"
> +#endif

Maybe this is my kernel taste leaking through, but I am allergic to
ifdef in ".c" files. In this case you could move the include of
tracefs.h into event_trace.h and then ifdef guard all the parts of
event_trace.h that need tracefs.h.

>  
>  #include "filter.h"
>  #include "json.h"
>  #include "../daxctl/json.h"
> -#include "../util/event_trace.h"
>  
>  #define CXL_FW_VERSION_STR_LEN	16
>  #define CXL_FW_MAX_SLOTS	4
> @@ -575,6 +578,7 @@ err_jobj:
>  	return NULL;
>  }
>  
> +#ifdef ENABLE_LIBTRACEFS
>  /* CXL Spec 3.1 Table 8-140 Media Error Record */
>  #define CXL_POISON_SOURCE_MAX 7
>  static const char *const poison_source[] = { "Unknown", "External", "Internal",
> @@ -753,6 +757,15 @@ err_free:
>  	tracefs_instance_free(inst);
>  	return jpoison;
>  }
> +#else
> +static struct json_object *
> +util_cxl_poison_list_to_json(struct cxl_region *region,
> +			     struct cxl_memdev *memdev,
> +			     unsigned long flags)
> +{
> +	return NULL;
> +}
> +#endif

This would move a new conditionally compiled ".c" file for just these
trace helpers.

>  struct json_object *util_cxl_memdev_to_json(struct cxl_memdev *memdev,
>  		unsigned long flags)
> diff --git a/cxl/list.c b/cxl/list.c
> index 0b25d78248d5..48bd1ebc3c0e 100644
> --- a/cxl/list.c
> +++ b/cxl/list.c
> @@ -146,6 +146,12 @@ int cmd_list(int argc, const char **argv, struct cxl_ctx *ctx)
>  		param.ctx.log_priority = LOG_DEBUG;
>  	}
>  
> +#ifndef ENABLE_LIBTRACEFS
> +	if (param.media_errors) {
> +		notice(&param, "--media-errors support disabled at build time\n");
> +		param.media_errors = false;
> +	}
> +#endif

This would be a static inline helper in a header file that optionally
reports the problem.

All that said, I am not the maintainer so go with what you want, but
leaking ifdef in ".c" is, in my opinion, a slow walk into an
increasingly unreadable code base.