Add an option namely --input which passes a parameter
which is a JSON file path. The JSON file contains the
data usually returned by:

        $ daxctl list -d dax0.1 | jq -er '.[]' > device.json
        {
          "chardev":"dax0.1",
          "size":34359738368,
          "target_node":0,
          "align":1073741824,
          "mode":"devdax",
          "mappings":[
            {
              "page_offset":4194304,
              "start":25769803776,
              "end":42949672959,
              "size":17179869184
            },
            {
              "page_offset":0,
              "start":8589934592,
              "end":25769803775,
              "size":17179869184
            }
          ]
        }

The input values in the mapping json are decimal
for now. A device can then be created by specifying this same data
to re-create it e.g.

        $ daxctl create-device -u --input device.json
        {
          "chardev":"dax0.1",
          "size":"32.00 GiB (34.36 GB)",
          "target_node":0,
          "align":"1024.00 MiB (1073.74 MB)",
          "mode":"devdax",
        }

        $ daxctl list -d dax0.1
        {
          "chardev":"dax0.1",
          "size":34359738368,
          "target_node":0,
          "align":1073741824,
          "mode":"devdax",
          "mappings":[
            {
              "page_offset":4194304,
              "start":25769803776,
              "end":42949672959,
              "size":17179869184
            },
            {
              "page_offset":0,
              "start":8589934592,
              "end":25769803775,
              "size":17179869184
            }
          ]
        }

        created 1 device

This means we can restore/recreate previously established mappings.

Signed-off-by: Joao Martins <joao.m.mart...@oracle.com>
---
 Documentation/daxctl/daxctl-create-device.txt |  13 +++
 daxctl/device.c                               | 128 +++++++++++++++++++++++++-
 2 files changed, 136 insertions(+), 5 deletions(-)

diff --git a/Documentation/daxctl/daxctl-create-device.txt 
b/Documentation/daxctl/daxctl-create-device.txt
index 7f64719d16f2..05f4dbd9d61c 100644
--- a/Documentation/daxctl/daxctl-create-device.txt
+++ b/Documentation/daxctl/daxctl-create-device.txt
@@ -90,6 +90,19 @@ include::region-option.txt[]
        to 2M. Note that "devdax" mode enforces all mappings to be
        aligned to this value, i.e. it fails unaligned mapping attempts.
 
+--input::
+       Applications that want to select ranges assigned to a device-dax
+       instance, or wanting to establish previously created devices, can
+       pass an input JSON file. The file option lets a user pass a JSON
+       object similar to the one listed with "daxctl list".
+
+       The device name is not re-created, but if a "chardev" is passed in
+       the JSON file, it will use that to get the region id.
+
+       Note that the JSON content in the file cannot be an array of
+       JSON objects but rather a single JSON object i.e. without the
+       array enclosing brackets.
+
 include::human-option.txt[]
 
 include::verbose-option.txt[]
diff --git a/daxctl/device.c b/daxctl/device.c
index 3c2d4e3d8b48..fe4291199312 100644
--- a/daxctl/device.c
+++ b/daxctl/device.c
@@ -13,6 +13,7 @@
 #include <util/json.h>
 #include <util/filter.h>
 #include <json-c/json.h>
+#include <json-c/json_util.h>
 #include <daxctl/libdaxctl.h>
 #include <util/parse-options.h>
 #include <ccan/array_size/array_size.h>
@@ -23,6 +24,7 @@ static struct {
        const char *region;
        const char *size;
        const char *align;
+       const char *input;
        bool no_online;
        bool no_movable;
        bool force;
@@ -36,10 +38,16 @@ enum dev_mode {
        DAXCTL_DEV_MODE_RAM,
 };
 
+struct mapping {
+       unsigned long long start, end, pgoff;
+};
+
 static enum dev_mode reconfig_mode = DAXCTL_DEV_MODE_UNKNOWN;
 static long long align = -1;
 static long long size = -1;
 static unsigned long flags;
+static struct mapping *maps = NULL;
+static long long nmaps = -1;
 
 enum memory_zone {
        MEM_ZONE_MOVABLE,
@@ -71,7 +79,8 @@ OPT_BOOLEAN('f', "force", &param.force, \
 
 #define CREATE_OPTIONS() \
 OPT_STRING('s', "size", &param.size, "size", "size to switch the device to"), \
-OPT_STRING('a', "align", &param.align, "align", "alignment to switch the 
device to")
+OPT_STRING('a', "align", &param.align, "align", "alignment to switch the 
device to"), \
+OPT_STRING('\0', "input", &param.input, "input", "input device JSON file")
 
 #define DESTROY_OPTIONS() \
 OPT_BOOLEAN('f', "force", &param.force, \
@@ -124,6 +133,94 @@ static const struct option destroy_options[] = {
        OPT_END(),
 };
 
+static int sort_mappings(const void *a, const void *b)
+{
+       json_object **jsoa, **jsob;
+       struct json_object *va, *vb;
+       unsigned long long pga, pgb;
+
+       jsoa = (json_object **)a;
+       jsob = (json_object **)b;
+       if (!*jsoa && !*jsob)
+               return 0;
+
+       if (!json_object_object_get_ex(*jsoa, "page_offset", &va) ||
+           !json_object_object_get_ex(*jsob, "page_offset", &vb))
+               return 0;
+
+       pga = json_object_get_int64(va);
+       pgb = json_object_get_int64(vb);
+
+       return pga > pgb;
+}
+
+static int parse_device_file(const char *filename)
+{
+       struct json_object *jobj, *jval = NULL, *jmappings = NULL;
+       int i, len, rc = -EINVAL, region_id, id;
+       const char *chardev;
+       char  *region = NULL;
+       struct mapping *m;
+
+       jobj = json_object_from_file(filename);
+       if (!jobj)
+               return rc;
+
+       if (!json_object_object_get_ex(jobj, "align", &jval))
+               return rc;
+       param.align = json_object_get_string(jval);
+
+       if (!json_object_object_get_ex(jobj, "size", &jval))
+               return rc;
+       param.size = json_object_get_string(jval);
+
+       if (!json_object_object_get_ex(jobj, "chardev", &jval))
+               return rc;
+       chardev = json_object_get_string(jval);
+       if (sscanf(chardev, "dax%u.%u", &region_id, &id) != 2)
+               return rc;
+       if (asprintf(&region, "%u", region_id) < 0)
+               return rc;
+       param.region = region;
+
+       if (!json_object_object_get_ex(jobj, "mappings", &jmappings))
+               return rc;
+       json_object_array_sort(jmappings, sort_mappings);
+
+       len = json_object_array_length(jmappings);
+       m = calloc(len, sizeof(*m));
+       if (!m)
+               return -ENOMEM;
+
+       for (i = 0; i < len; i++) {
+               struct json_object *j, *val;
+
+               j = json_object_array_get_idx(jmappings, i);
+               if (!j)
+                       goto err;
+
+               if (!json_object_object_get_ex(j, "start", &val))
+                       goto err;
+               m[i].start = json_object_get_int64(val);
+
+               if (!json_object_object_get_ex(j, "end", &val))
+                       goto err;
+               m[i].end = json_object_get_int64(val);
+
+               if (!json_object_object_get_ex(j, "page_offset", &val))
+                       goto err;
+               m[i].pgoff = json_object_get_int64(val);
+       }
+       maps = m;
+       nmaps = len;
+       rc = 0;
+
+err:
+       if (!maps)
+               free(m);
+       return rc;
+}
+
 static const char *parse_device_options(int argc, const char **argv,
                enum device_action action, const struct option *options,
                const char *usage, struct daxctl_ctx *ctx)
@@ -214,6 +311,13 @@ static const char *parse_device_options(int argc, const 
char **argv,
                }
                break;
        case ACTION_CREATE:
+               if (param.input &&
+                   (rc = parse_device_file(param.input)) != 0) {
+                       fprintf(stderr,
+                               "error: failed to parse device file: %s\n",
+                               strerror(-rc));
+                       break;
+               }
                if (param.size)
                        size = __parse_size64(param.size, &units);
                if (param.align)
@@ -525,7 +629,8 @@ static int do_create(struct daxctl_region *region, long 
long val,
 {
        struct json_object *jdev;
        struct daxctl_dev *dev;
-       int rc = 0;
+       int i, rc = 0;
+       long long alloc = 0;
 
        if (daxctl_region_create_dev(region))
                return -ENOSPC;
@@ -546,9 +651,22 @@ static int do_create(struct daxctl_region *region, long 
long val,
                        return rc;
        }
 
-       rc = daxctl_dev_set_size(dev, val);
-       if (rc < 0)
-               return rc;
+       /* @maps is ordered by page_offset */
+       for (i = 0; i < nmaps; i++) {
+               rc = daxctl_dev_set_mapping(dev, maps[i].start, maps[i].end);
+               if (rc < 0)
+                       return rc;
+               alloc += (maps[i].end - maps[i].start + 1);
+       }
+
+       if (nmaps > 0 && val > 0 && alloc != val) {
+               fprintf(stderr, "%s: allocated %lld but specified size %lld\n",
+                       daxctl_dev_get_devname(dev), alloc, val);
+       } else {
+               rc = daxctl_dev_set_size(dev, val);
+               if (rc < 0)
+                       return rc;
+       }
 
        rc = daxctl_dev_enable_devdax(dev);
        if (rc) {
-- 
1.8.3.1
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