On Tue, Jul 09, 2024 at 11:39:08PM +0200, Martin Wilck wrote:
This is a great idea! I just have a few minor issues.
> libmp_mapinfo() is intended as a generic abstraction for retrieving information from
> the kernel device-mapper driver. It retrieves the information that the caller
> needs, with a minimal set of DM ioctls, and never more then 2 ioctl calls.
>
> libdm's DM_DEVICE_TABLE and DM_DEVICE_STATUS calls map to the kernel's
> DM_TABLE_STATUS ioctl, with or without the DM_STATUS_TABLE_FLAG set,
> respectively. DM_TABLE_STATUS always retrieves the basic map status (struct
> dm_info) and the map UUID and name, too.
>
> Note: I'd prefer to use an unnamed struct instead of _u in
> union libmp_map_identifer. But doing using an unnamed struct and and
> initializing the union like this in a function argument:
>
> func((mapid_t) { .major = major, .minor = minor })
This is a nitpick, but instead of using _u, couldn't you just pass the
major and minor as a dev_t? If you're working with an actual major and
minor, you would need to do something like:
(mapid_t) { .dev = makedev(major, minor) }
but we are often already dealing with a dev_t, so instead of doing:
(mapid_t) { ._u = { major(dev), minor(dev) } }
we could just do:
(mapid_t) { .dev = dev }
To get the major and minor out in the libmp_mapinfo() you would need to
use major(id.dev) and minor(id.dev), instead of id._u.major and
id._u.minor, but I think first set is more readable anyway.
>
> is not part of C99, and not supported in gcc 4.8, which we still support.
>
> Likewise, the following syntax for initializing an empty struct:
>
> (mapinfo_t) { 0 }
>
> is not supported on all architectures we support (notably clang 3.5 under
> Debian Jessie).
>
> Signed-off-by: Martin Wilck <mwilck@xxxxxxxx>
> ---
> libmultipath/devmapper.c | 181 +++++++++++++++++++++++++++++-
> libmultipath/devmapper.h | 66 +++++++++++
> libmultipath/libmultipath.version | 3 +-
> 3 files changed, 248 insertions(+), 2 deletions(-)
>
> diff --git a/libmultipath/devmapper.c b/libmultipath/devmapper.c
> index 3685ef7..5c9f9d8 100644
> --- a/libmultipath/devmapper.c
> +++ b/libmultipath/devmapper.c
> @@ -14,7 +14,6 @@
> #include <errno.h>
> #include <syslog.h>
> #include <sys/sysmacros.h>
> -#include <linux/dm-ioctl.h>
>
> #include "util.h"
> #include "vector.h"
> @@ -604,6 +603,186 @@ has_dm_info(const struct multipath *mpp)
> return (mpp && mpp->dmi.exists != 0);
> }
>
> +static int libmp_set_map_identifier(int flags, mapid_t id, struct dm_task *dmt)
> +{
> + switch (flags & __DM_MAP_BY_MASK) {
> + case DM_MAP_BY_UUID:
> + if (!id.str || !(*id.str))
> + return 0;
> + return dm_task_set_uuid(dmt, id.str);
> + case DM_MAP_BY_NAME:
> + if (!id.str || !(*id.str))
> + return 0;
> + return dm_task_set_name(dmt, id.str);
> + case DM_MAP_BY_DEV:
> + if (!dm_task_set_major(dmt, id._u.major))
> + return 0;
> + return dm_task_set_minor(dmt, id._u.minor);
> + default:
> + condlog(0, "%s: invalid by_id", __func__);
> + return 0;
> + }
> +}
> +
> +static int libmp_mapinfo__(int flags, mapid_t id, mapinfo_t info, const char *map_id)
> +{
> + struct dm_task __attribute__((cleanup(cleanup_dm_task))) *dmt = NULL;
> + struct dm_info dmi;
> + int rc, ioctl_nr;
> + uint64_t start, length = 0;
> + char *target_type = NULL, *params = NULL;
> + const char *name = NULL, *uuid = NULL;
> + char __attribute__((cleanup(cleanup_charp))) *tmp_target = NULL;
> + char __attribute__((cleanup(cleanup_charp))) *tmp_status = NULL;
> + bool tgt_set = false;
> +
> + /*
> + * If both info.target and info.status are set, we need two
> + * ioctls. Call this function recursively.
> + * If successful, tmp_target will be non-NULL.
> + */
> + if (info.target && info.status) {
> + rc = libmp_mapinfo__(flags, id,
> + (mapinfo_t) {
> + .target = &tmp_target,
> + .tgt_type = info.tgt_type,
> + },
> + map_id);
> + if (rc != DMP_OK)
> + return rc;
> + tgt_set = true;
> + }
> +
> + /*
> + * The DM_DEVICE_TABLE and DM_DEVICE_STATUS ioctls both fetch the basic
> + * information from DM_DEVICE_INFO, too.
> + * Choose the most lightweight ioctl to fetch all requested info.
> + */
> + if (info.target && !info.status)
> + ioctl_nr = DM_DEVICE_TABLE;
> + else if (info.status || info.size || info.tgt_type)
> + ioctl_nr = DM_DEVICE_STATUS;
> + else
> + ioctl_nr = DM_DEVICE_INFO;
> +
> + if (!(dmt = libmp_dm_task_create(ioctl_nr)))
> + return DMP_ERR;
> +
> + if (!libmp_set_map_identifier(flags, id, dmt)) {
> + condlog(2, "%s: failed to set map identifier to %s", __func__, map_id);
> + return DMP_ERR;
> + }
> +
> + if (!libmp_dm_task_run(dmt)) {
> + dm_log_error(3, ioctl_nr, dmt);
> + if (dm_task_get_errno(dmt) == ENXIO) {
> + condlog(2, "%s: map %s not found", __func__, map_id);
> + return DMP_NOT_FOUND;
> + } else
> + return DMP_ERR;
> + }
> +
> + condlog(4, "%s: DM ioctl %d succeeded for %s",
> + __func__, ioctl_nr, map_id);
> +
> + if (!dm_task_get_info(dmt, &dmi) || !dmi.exists) {
> + condlog(2, "%s: map %s doesn't exist", __func__, map_id);
> + return DMP_NOT_FOUND;
> + }
> +
> + if (info.target || info.status || info.size || info.tgt_type) {
> + if (dm_get_next_target(dmt, NULL, &start, &length,
> + &target_type, ¶ms) != NULL) {
> + condlog(2, "%s: map %s has multiple targets", __func__, map_id);
> + return DMP_NOT_FOUND;
> + }
> + if (!params) {
> + condlog(2, "%s: map %s has no targets", __func__, map_id);
> + return DMP_NOT_FOUND;
> + }
> + if (info.tgt_type && strcmp(info.tgt_type, target_type)) {
> + condlog(3, "%s: target type mismatch: \"%s\" != \"%s\"",
> + __func__, info.tgt_type, target_type);
> + return DMP_NO_MATCH;
> + }
> + }
> +
> + /*
> + * Check possible error conditions.
> + * If error is returned, don't touch any output parameters.
> + */
> + if ((info.name && !(name = dm_task_get_name(dmt)))
> + || (info.uuid && !(uuid = dm_task_get_uuid(dmt)))
> + || (info.status && !(tmp_status = strdup(params)))
> + || (info.target && !tmp_target && !(tmp_target = strdup(params))))
> + return DMP_ERR;
> +
> + if (info.name) {
> + strlcpy(info.name, name, WWID_SIZE);
> + condlog(4, "%s: %s: name: \"%s\"", __func__, map_id, info.name);
> + }
> + if (info.uuid) {
> + strlcpy(info.uuid, uuid, DM_UUID_LEN);
> + condlog(4, "%s: %s: uuid: \"%s\"", __func__, map_id, info.uuid);
> + }
> +
> + if (info.size) {
> + *info.size = length;
> + condlog(4, "%s: %s: size: %lld", __func__, map_id, *info.size);
> + }
> +
> + if (info.dmi) {
> + memcpy(info.dmi, &dmi, sizeof(*info.dmi));
> + condlog(4, "%s: %s %d:%d, %d targets, %s table, %s, %s, %d opened, %u events",
> + __func__, map_id,
> + info.dmi->major, info.dmi->minor,
> + info.dmi->target_count,
> + info.dmi->live_table ? "live" :
> + info.dmi->inactive_table ? "inactive" : "no",
> + info.dmi->suspended ? "suspended" : "active",
> + info.dmi->read_only ? "ro" : "rw",
> + info.dmi->open_count,
> + info.dmi->event_nr);
> + }
> +
> + if (info.target) {
> + *info.target = steal_ptr(tmp_target);
> + if (!tgt_set)
> + condlog(4, "%s: %s: target: \"%s\"", __func__, map_id, *info.target);
> + }
> +
> + if (info.status) {
> + *info.status = steal_ptr(tmp_status);
> + condlog(4, "%s: %s: status: \"%s\"", __func__, map_id, *info.status);
> + }
> +
> + return DMP_OK;
> +}
> +
> +/* Helper: format a string describing the map for log messages */
> +static const char* libmp_map_identifier(int flags, mapid_t id, char buf[BLK_DEV_SIZE])
> +{
> + switch (flags & __DM_MAP_BY_MASK) {
> + case DM_MAP_BY_NAME:
> + case DM_MAP_BY_UUID:
> + return id.str;
> + case DM_MAP_BY_DEV:
> + safe_snprintf(buf, BLK_DEV_SIZE, "%d:%d", id._u.major, id._u.minor);
> + return buf;
> + default:
> + safe_snprintf(buf, BLK_DEV_SIZE, "*invalid*");
> + return buf;
> + }
> +}
> +
> +int libmp_mapinfo(int flags, mapid_t id, mapinfo_t info)
> +{
> + char idbuf[BLK_DEV_SIZE];
> +
> + return libmp_mapinfo__(flags, id, info,
> + libmp_map_identifier(flags, id, idbuf));
> +}
> +
> int
> dm_get_info(const char *name, struct dm_info *info)
> {
> diff --git a/libmultipath/devmapper.h b/libmultipath/devmapper.h
> index 9438c2d..269389b 100644
> --- a/libmultipath/devmapper.h
> +++ b/libmultipath/devmapper.h
> @@ -1,5 +1,6 @@
> #ifndef _DEVMAPPER_H
> #define _DEVMAPPER_H
> +#include <linux/dm-ioctl.h>
> #include "autoconfig.h"
> #include "structs.h"
>
> @@ -31,8 +32,73 @@ enum {
> DMP_ERR,
> DMP_OK,
> DMP_NOT_FOUND,
> + DMP_NO_MATCH,
> };
>
> +/**
> + * enum mapinfo_flags: input flags for libmp_mapinfo()
> + */
> +enum __mapinfo_flags {
> + /** DM_MAP_BY_NAME: identify map by device-mapper name from @name */
> + DM_MAP_BY_NAME = 0,
> + /** DM_MAP_BY_UUID: identify map by device-mapper UUID from @uuid */
> + DM_MAP_BY_UUID,
> + /** DM_MAP_BY_DEV: identify map by major/minor number from @dmi */
> + DM_MAP_BY_DEV,
> + __DM_MAP_BY_MASK = (1 << 3) - 1,
I assume you orignally indented these to be flags, but they aren't
really, so __DM_MAP_BY_MASK would just be 3, since the values are 0, 1,
and 2.
> +};
> +
> +typedef union libmp_map_identifier {
> + const char *str;
Like I said before, I would just use
dev_t dev;
instead of the struct. But I don't have stong feelings about this if you
prefer keeping major and minor separate.
> + struct {
> + int major;
> + int minor;
> + } _u;
> +} mapid_t;
> +
> +typedef struct libmp_map_info {
> + /** @name: name of the map.
> + * If non-NULL, it must point to an array of WWID_SIZE bytes
> + */
> + char *name;
> + /** @uuid: UUID of the map.
> + * If non-NULL it must point to an array of DM_UUID_LEN bytes
> + */
> + char *uuid;
> + /** @dmi: Basic info, must point to a valid dm_info buffer if non-NULL */
> + struct dm_info *dmi;
> + /** @target: target params, *@target will be allocated if @target is non-NULL*/
> + char **target;
> + /** @size: target size. Will be ignored if @target is NULL */
> + unsigned long long *size;
> + /** @status: target status, *@status will be allocated if @status is non-NULL */
> + char **status;
> + /** @tgt_type: (input) set to a target type, e.g. "multipath" to limit
> + * successful return to just this target type in libmp_mapinfo().
> + */
> + const char *tgt_type;
> +} mapinfo_t;
> +
> +/**
> + * libmp_mapinfo(): obtain information about a map from the kernel
> + * @param flags: see __mapinfo_flags above.
> + * Exactly one of DM_MAP_BY_NAME, DM_MAP_BY_UUID, and DM_MAP_BY_DEV must be set.
Again, you can't really set multiple values, so this comment doesn't
make sense.
-Ben
> + * @param id: string or major/minor to identify the map to query
> + * @param info: output parameters, see above. Non-NULL elements will be filled in.
> + * @returns:
> + * DMP_OK if successful.
> + * DMP_NOT_FOUND if the map wasn't found, or has no or multiple targets.
> + * DMP_NO_MATCH if the map didn't match @tgt_type (see above).
> + * DMP_ERR if some other error occurred.
> + *
> + * This function obtains the requested information for the device-mapper map
> + * identified by the input parameters.
> + * Output parameters are only filled in if the return value is DMP_OK.
> + * For target / status / size information, the map's table should contain
> + * only one target (usually multipath or linear).
> + */
> +int libmp_mapinfo(int flags, mapid_t id, mapinfo_t info);
> +
> int dm_prereq(unsigned int *v);
> void skip_libmp_dm_init(void);
> void libmp_dm_exit(void);
> diff --git a/libmultipath/libmultipath.version b/libmultipath/libmultipath.version
> index f58cb1d..48c2b67 100644
> --- a/libmultipath/libmultipath.version
> +++ b/libmultipath/libmultipath.version
> @@ -43,7 +43,7 @@ LIBMPATHCOMMON_1.0.0 {
> put_multipath_config;
> };
>
> -LIBMULTIPATH_24.0.0 {
> +LIBMULTIPATH_25.0.0 {
> global:
> /* symbols referenced by multipath and multipathd */
> add_foreign;
> @@ -134,6 +134,7 @@ global:
> libmp_get_version;
> libmp_get_multipath_config;
> libmp_dm_task_run;
> + libmp_mapinfo;
> libmp_put_multipath_config;
> libmp_udev_set_sync_support;
> libmultipath_exit;
> --
> 2.45.2
