Re: [NDCTL PATCH v4 2/3] cxl: Enumerate major/minor of FWCTL char device

[Alison Schofield <alison.schofield@intel.com>]

On Tue, Feb 18, 2025 at 03:59:55PM -0700, Dave Jiang wrote:
> Add major/minor discovery for the FWCTL character device that is associated
> with supprting CXL Features under the cxl_memdev. Add libcxl API functions
> to retrieve the major and minor of the FWCTL character device.
> 
> Signed-off-by: Dave Jiang <dave.jiang@intel.com>
> ---
>  cxl/lib/libcxl.c   | 74 ++++++++++++++++++++++++++++++++++++++++++++++
>  cxl/lib/libcxl.sym |  2 ++
>  cxl/lib/private.h  |  1 +
>  cxl/libcxl.h       |  2 ++
>  4 files changed, 79 insertions(+)

Please describe the new library interface in 
"Documentation/cxl/lib/libcxl.txt"

Add To: nvdimm@lists.linux.dev

> 
> diff --git a/cxl/lib/libcxl.c b/cxl/lib/libcxl.c
> index bab7343e8a4a..566870acb30a 100644
> --- a/cxl/lib/libcxl.c
> +++ b/cxl/lib/libcxl.c
> @@ -1253,6 +1253,66 @@ static int add_cxl_memdev_fwl(struct cxl_memdev *memdev,
>  	return -ENOMEM;
>  }
>  


Can we define like this:
#define CXL_PATH_MAX 512

and do this:
char path[CXL_PATH_MAX];

in next 2 funcs?

> +static const char fwctl_prefix[] = "fwctl";
> +static int get_feature_chardev(const char *base, char *chardev_path)
> +{
> +	char *path = calloc(1, strlen(base) + 100);
> +	struct dirent *entry;
> +	int rc = 0;
> +	DIR *dir;
> +
> +	if (!path)
> +		return -ENOMEM;
> +
> +	sprintf(path, "%s/fwctl/", base);
> +	dir = opendir(path);
> +	if (!dir) {
> +		rc = -errno;
> +		goto err;
> +	}
> +
> +	while ((entry = readdir(dir)) != NULL)
> +		if (strncmp(entry->d_name, fwctl_prefix, strlen(fwctl_prefix)) == 0)
> +			break;

Can we exit this while loop w entry not NULL, yet not a match?
Maybe a found flag or store a match separately.

> +
> +	if (!entry) {
> +		rc = -ENOENT;
> +		goto read_err;
> +	}
> +
> +	sprintf(chardev_path, "/dev/fwctl/%s", entry->d_name);
> +
> +read_err:
> +	closedir(dir);
> +err:
> +	free(path);
> +	return rc;
> +}
> +
> +static int memdev_get_fwctl_chardev(struct cxl_memdev *memdev,
> +				    const char *cxlmem_base)
> +{
> +	char *path = calloc(1, strlen(cxlmem_base) + 100);
> +	struct stat st;
> +	int rc;
> +

Do we need to init memdev->fwctl... to something to avoid garbage?


> +	rc = get_feature_chardev(cxlmem_base, path);
> +	if (rc)
> +		goto out;
> +
> +	if (stat(path, &st) < 0) {
> +		rc = -errno;
> +		goto out;
> +	}
> +
> +	memdev->fwctl_major = major(st.st_rdev);
> +	memdev->fwctl_minor = minor(st.st_rdev);
> +
> +out:
> +	free(path);
> +	return rc;
> +}
> +
>  static void *add_cxl_memdev(void *parent, int id, const char *cxlmem_base)
>  {
>  	const char *devname = devpath_to_devname(cxlmem_base);
> @@ -1279,6 +1339,10 @@ static void *add_cxl_memdev(void *parent, int id, const char *cxlmem_base)
>  	memdev->major = major(st.st_rdev);
>  	memdev->minor = minor(st.st_rdev);
>  
> +	/* If this fails, no Features support. */
> +	if (memdev_get_fwctl_chardev(memdev, cxlmem_base))
> +		dbg(ctx, "%s: no Features support.\n", devname);
> +
>  	sprintf(path, "%s/pmem/size", cxlmem_base);
>  	if (sysfs_read_attr(ctx, path, buf) == 0)
>  		memdev->pmem_size = strtoull(buf, NULL, 0);
> @@ -1515,6 +1579,16 @@ CXL_EXPORT int cxl_memdev_get_minor(struct cxl_memdev *memdev)
>  	return memdev->minor;
>  }
>  
> +CXL_EXPORT int cxl_memdev_get_fwctl_major(struct cxl_memdev *memdev)
> +{
> +	return memdev->fwctl_major;
> +}
> +
> +CXL_EXPORT int cxl_memdev_get_fwctl_minor(struct cxl_memdev *memdev)
> +{
> +	return memdev->fwctl_minor;
> +}
> +
>  CXL_EXPORT unsigned long long cxl_memdev_get_pmem_size(struct cxl_memdev *memdev)
>  {
>  	return memdev->pmem_size;
> diff --git a/cxl/lib/libcxl.sym b/cxl/lib/libcxl.sym
> index 1fc33cc6e1a4..b2b51a72673c 100644
> --- a/cxl/lib/libcxl.sym
> +++ b/cxl/lib/libcxl.sym
> @@ -292,4 +292,6 @@ global:
>  LIBCXL_9 {
>  global:
>  	cxl_bus_get_by_provider;
> +	cxl_memdev_get_fwctl_major;
> +	cxl_memdev_get_fwctl_minor;
>  } LIBECXL_8;
> diff --git a/cxl/lib/private.h b/cxl/lib/private.h
> index b6cd910e9335..676bf1573487 100644
> --- a/cxl/lib/private.h
> +++ b/cxl/lib/private.h
> @@ -37,6 +37,7 @@ enum cxl_fwl_loading {
>  struct cxl_endpoint;
>  struct cxl_memdev {
>  	int id, major, minor;
> +	int fwctl_major, fwctl_minor;
>  	int numa_node;
>  	void *dev_buf;
>  	size_t buf_len;
> diff --git a/cxl/libcxl.h b/cxl/libcxl.h
> index 3b309968a808..26aa906740af 100644
> --- a/cxl/libcxl.h
> +++ b/cxl/libcxl.h
> @@ -69,6 +69,8 @@ const char *cxl_memdev_get_host(struct cxl_memdev *memdev);
>  struct cxl_bus *cxl_memdev_get_bus(struct cxl_memdev *memdev);
>  int cxl_memdev_get_major(struct cxl_memdev *memdev);
>  int cxl_memdev_get_minor(struct cxl_memdev *memdev);
> +int cxl_memdev_get_fwctl_major(struct cxl_memdev *memdev);
> +int cxl_memdev_get_fwctl_minor(struct cxl_memdev *memdev);
>  struct cxl_ctx *cxl_memdev_get_ctx(struct cxl_memdev *memdev);
>  unsigned long long cxl_memdev_get_pmem_size(struct cxl_memdev *memdev);
>  unsigned long long cxl_memdev_get_ram_size(struct cxl_memdev *memdev);
> -- 
> 2.48.1
>