Hi Ondřej,
On Thu, 7 Nov 2019 15:00:06 +0100, Ondřej Lysoněk wrote:
> The i2c-dev kernel module is necessary to access I2C adapters from
> userspace, so it's needed by all the I2C tools. The module is not
> loaded automatically, so when e.g. i2cdetect is run without i2c-dev
> loaded, it gives a false impression that no I2C adapters exist, which
> is not very user-friendly:
>
> # i2cdetect -l
> # modprobe i2c-dev
> # i2cdetect -l
> i2c-0 i2c i915 gmbus ssc I2C adapter
> i2c-1 i2c i915 gmbus vga I2C adapter
> i2c-2 i2c i915 gmbus panel I2C adapter
> i2c-3 i2c i915 gmbus dpc I2C adapter
> i2c-4 i2c i915 gmbus dpb I2C adapter
> i2c-5 i2c i915 gmbus dpd I2C adapter
> i2c-6 i2c DPDDC-C I2C adapter
> i2c-7 i2c DPDDC-D I2C adapter
Yeah, I agree, I meant to do this for a long time, actually I have a
proof-of-concept patch for this on my disk from 2006 :-(
> This patch makes all the tools autoload i2c-dev when needed. The code
> to load the module is compiled in only if libkmod is present on the
> system.
What is the added value of libkmod here? I mean, how is this any better
than:
system("modprobe i2c-dev");
which is what my patch was doing?
> This resolves the following Fedora bug:
> https://bugzilla.redhat.com/show_bug.cgi?id=913203
>
> The patch is based on a previous version of the patch by Michal Minar,
> posted on linux-i2c some time ago:
> https://marc.info/?l=linux-i2c&m=140195625915505&w=2
>
> The patch is also inspired by the GPLv2+ modprobe from kmod.
>
> Signed-off-by: Ondřej Lysoněk <olysonek@xxxxxxxxxx>
> ---
> tools/Module.mk | 11 +++++-
> tools/i2cbusses.c | 97 +++++++++++++++++++++++++++++++++++++++++------
> 2 files changed, 95 insertions(+), 13 deletions(-)
>
> diff --git a/tools/Module.mk b/tools/Module.mk
> index 693102f..17ef8d4 100644
> --- a/tools/Module.mkles joues
> +++ b/tools/Module.mk
> @@ -12,10 +12,17 @@ TOOLS_DIR := tools
> TOOLS_CFLAGS := -Wstrict-prototypes -Wshadow -Wpointer-arith -Wcast-qual \
> -Wcast-align -Wwrite-strings -Wnested-externs -Winline \
> -W -Wundef -Wmissing-prototypes -Iinclude
> +TOOLS_LDFLAGS :=
> +
> +ifeq ($(shell pkg-config --exists libkmod && echo 1), 1)
> +TOOLS_CFLAGS += $(shell pkg-config --cflags libkmod) -DUSE_LIBKMOD
> +TOOLS_LDFLAGS += $(shell pkg-config --libs libkmod)
> +endif
> +
> ifeq ($(USE_STATIC_LIB),1)
> -TOOLS_LDFLAGS := $(LIB_DIR)/$(LIB_STLIBNAME)
> +TOOLS_LDFLAGS += $(LIB_DIR)/$(LIB_STLIBNAME)
> else
> -TOOLS_LDFLAGS := -L$(LIB_DIR) -li2c
> +TOOLS_LDFLAGS += -L$(LIB_DIR) -li2c
> endif
>
> TOOLS_TARGETS := i2cdetect i2cdump i2cset i2cget i2ctransfer
> diff --git a/tools/i2cbusses.c b/tools/i2cbusses.c
> index b4f00ae..5f3ad42 100644
> --- a/tools/i2cbusses.c
> +++ b/tools/i2cbusses.c
> @@ -43,6 +43,14 @@
> #include <linux/i2c.h>
> #include <linux/i2c-dev.h>
>
> +#ifdef USE_LIBKMOD
> +#include <libkmod.h>
> +
> +#define I2C_DEV_MOD_NAME "i2c_dev"
> +#define MODULE_LOAD_ERR_MSG "Error: Failed to load required " \
> + I2C_DEV_MOD_NAME " kernel module: "
> +#endif
> +
> enum adt { adt_dummy, adt_isa, adt_i2c, adt_smbus, adt_unknown };
>
> struct adap_type {
> @@ -63,6 +71,61 @@ static struct adap_type adap_types[5] = {
> .algo = "N/A", },
> };
>
> +
> +/**
> + * Try to load the i2c_dev kernel module.
> + * Returns 1 on success, 0 otherwise.
> + */
> +static int load_i2c_dev_module(int quiet) {
> + int ret = 0;
> +#ifdef USE_LIBKMOD
> + int flags = 0;
> + struct kmod_ctx *ctx;
> + struct kmod_list *l, *list = NULL;
> +
> + ctx = kmod_new(NULL, NULL);
> + if (!ctx) {
> + if (!quiet)
> + fprintf(stderr,
> + MODULE_LOAD_ERR_MSG "kmod_new() failed\n");
> + goto out;
> + }
> + if (kmod_module_new_from_lookup(ctx, I2C_DEV_MOD_NAME, &list) < 0
> + || list == NULL) {
> + if (!quiet)
> + fprintf(stderr, MODULE_LOAD_ERR_MSG
> + I2C_DEV_MOD_NAME " module lookup failed\n");
> + goto ctx_unref;
> + }
> +
> + flags |= KMOD_PROBE_APPLY_BLACKLIST_ALIAS_ONLY;
> + kmod_list_foreach(l, list) {
> + struct kmod_module *mod = kmod_module_get_module(l);
> + int res;
> + res = kmod_module_probe_insert_module(mod, flags, NULL, NULL,
> + NULL, NULL);
> + ret = (res >= 0);
> + if (res == -ENOENT && !quiet) {
> + fprintf(stderr, MODULE_LOAD_ERR_MSG
> + "unknown symbol in module \"%s\", or unknown parameter (see dmesg)\n",
> + kmod_module_get_name(mod));
> + } else if (res < 0 && !quiet) {
> + fprintf(stderr, MODULE_LOAD_ERR_MSG "(module %s): %s\n",
> + kmod_module_get_name(mod), strerror(-res));
> + }
> + kmod_module_unref(mod);
> + }
> +
> + kmod_module_unref_list(list);
> +ctx_unref:
> + kmod_unref(ctx);
> +out:
> +#else
> + (void) quiet;
> +#endif
> + return ret;
> +}
> +
> static enum adt i2c_get_funcs(int i2cbus)
> {
> unsigned long funcs;
> @@ -209,8 +272,12 @@ struct i2c_adap *gather_i2c_busses(void)
> i2c-dev and what we really care about are the i2c-dev numbers.
> Unfortunately the names are harder to get in i2c-dev */
> strcat(sysfs, "/class/i2c-dev");
> - if(!(dir = opendir(sysfs)))
> - goto done;
> + if(!(dir = opendir(sysfs))) {
> + if (!load_i2c_dev_module(0))
> + goto done;
> + if ((!(dir = opendir(sysfs))))
> + goto done;
> + }
> /* go through the busses */
> while ((de = readdir(dir)) != NULL) {
> if (!strcmp(de->d_name, "."))
> @@ -407,21 +474,29 @@ int parse_i2c_address(const char *address_arg, int all_addrs)
> int open_i2c_dev(int i2cbus, char *filename, size_t size, int quiet)
> {
> int file, len;
> + int i;
>
> - len = snprintf(filename, size, "/dev/i2c/%d", i2cbus);
> - if (len >= (int)size) {
> - fprintf(stderr, "%s: path truncated\n", filename);
> - return -EOVERFLOW;
> - }
> - file = open(filename, O_RDWR);
> -
> - if (file < 0 && (errno == ENOENT || errno == ENOTDIR)) {
> - len = snprintf(filename, size, "/dev/i2c-%d", i2cbus);
> + for (i = 0; i < 2; ++i) {
Sorry, what are you doing here?
> + len = snprintf(filename, size, "/dev/i2c/%d", i2cbus);
> if (len >= (int)size) {
> fprintf(stderr, "%s: path truncated\n", filename);
> return -EOVERFLOW;
> }
> file = open(filename, O_RDWR);
> +
> + if (file < 0 && (errno == ENOENT || errno == ENOTDIR)) {
> + len = snprintf(filename, size, "/dev/i2c-%d", i2cbus);
> + if (len >= (int)size) {
> + fprintf(stderr, "%s: path truncated\n", filename);
> + return -EOVERFLOW;
> + }
> + file = open(filename, O_RDWR);
> + }
> +
> + if (file >= 0 || (errno != ENOENT && errno != ENOTDIR))
> + break;
> + if (i > 0 || !load_i2c_dev_module(quiet))
> + break;
> }
>
> if (file < 0 && !quiet) {
--
Jean Delvare
SUSE L3 Support
