[PATCH v6 6/7] daxctl: Add --uuid option to create-device for sparse regions

[Anisa Su]

Add a --uuid option to 'daxctl create-device' that writes the given
uuid to the new dax device's sysfs 'uuid' attribute.  On sparse (DCD)
regions this claims dax_resources whose tag matches and populates the
seed device with their capacity; size is determined by the claim, so
--uuid is mutually exclusive with --size.

Pass "0" to claim a single untagged dax_resource.  A claim that
matches no dax_resource leaves the device at size 0; the kernel
returns ENOENT.

Plumb the write through a new daxctl_dev_set_uuid() libdaxctl helper
(LIBDAXCTL_11) and document the option in the man page.

Signed-off-by: Anisa Su <anisa.su887@xxxxxxxxx>
---
 Documentation/daxctl/daxctl-create-device.txt | 12 ++++
 daxctl/device.c                               | 72 +++++++++++++------
 daxctl/lib/libdaxctl.c                        | 44 ++++++++++++
 daxctl/lib/libdaxctl.sym                      |  5 ++
 daxctl/libdaxctl.h                            |  1 +
 5 files changed, 114 insertions(+), 20 deletions(-)

diff --git a/Documentation/daxctl/daxctl-create-device.txt b/Documentation/daxctl/daxctl-create-device.txt
index b774b86..27b87d0 100644
--- a/Documentation/daxctl/daxctl-create-device.txt
+++ b/Documentation/daxctl/daxctl-create-device.txt
@@ -82,6 +82,18 @@ include::region-option.txt[]
 
 	The size must be a multiple of the region alignment.
 
+	Mutually exclusive with --uuid.
+
+--uuid=::
+	For dax devices on sparse (DCD) regions, claim dax_resource(s) whose
+	tag matches the given UUID.  The device's size is determined by the
+	claimed capacity, so --uuid cannot be combined with --size.
+
+	A non-null UUID claims every matching dax_resource in the parent
+	region.  The value "0" is shorthand for the null UUID and claims a
+	single untagged dax_resource.  A write that matches no dax_resource
+	fails with ENOENT and the device is left at size 0.
+
 -a::
 --align::
 	Applications that want to establish dax memory mappings with
diff --git a/daxctl/device.c b/daxctl/device.c
index a4e36b1..21a941e 100644
--- a/daxctl/device.c
+++ b/daxctl/device.c
@@ -30,6 +30,7 @@ static struct {
 	const char *size;
 	const char *align;
 	const char *input;
+	const char *uuid;
 	bool check_config;
 	bool no_online;
 	bool no_movable;
@@ -85,7 +86,9 @@ OPT_BOOLEAN('C', "check-config", &param.check_config, \
 #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('\0', "input", &param.input, "input", "input device JSON file")
+OPT_STRING('\0', "input", &param.input, "input", "input device JSON file"), \
+OPT_STRING('\0', "uuid", &param.uuid, "uuid", \
+	"claim sparse dax_resource(s) matching this uuid (\"0\" for untagged)")
 
 #define DESTROY_OPTIONS() \
 OPT_BOOLEAN('f', "force", &param.force, \
@@ -808,6 +811,22 @@ static int do_create(struct daxctl_region *region, long long val,
 	struct daxctl_dev *dev;
 	int i, rc = 0;
 	long long alloc = 0;
+	uuid_t uuid;
+
+	if (param.uuid) {
+		if (param.size) {
+			fprintf(stderr,
+				"--uuid and --size are mutually exclusive\n");
+			return -EINVAL;
+		}
+		if (strcmp(param.uuid, "0") == 0) {
+			uuid_clear(uuid);
+		} else if (uuid_parse(param.uuid, uuid) < 0) {
+			fprintf(stderr, "failed to parse uuid '%s'\n",
+				param.uuid);
+			return -EINVAL;
+		}
+	}
 
 	if (daxctl_region_create_dev(region))
 		return -ENOSPC;
@@ -816,33 +835,46 @@ static int do_create(struct daxctl_region *region, long long val,
 	if (!dev)
 		return -ENOSPC;
 
-	if (val == -1)
-		val = daxctl_region_get_available_size(region);
-
-	if (val <= 0)
-		return -ENOSPC;
-
 	if (align > 0) {
 		rc = daxctl_dev_set_align(dev, align);
 		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)
+	if (param.uuid) {
+		rc = daxctl_dev_set_uuid(dev, uuid);
+		if (rc < 0) {
+			fprintf(stderr,
+				"%s: failed to claim uuid '%s': %s\n",
+				daxctl_dev_get_devname(dev), param.uuid,
+				strerror(-rc));
 			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;
+		if (val == -1)
+			val = daxctl_region_get_available_size(region);
+
+		if (val <= 0)
+			return -ENOSPC;
+
+		/* @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);
diff --git a/daxctl/lib/libdaxctl.c b/daxctl/lib/libdaxctl.c
index 02ae7e5..fe07939 100644
--- a/daxctl/lib/libdaxctl.c
+++ b/daxctl/lib/libdaxctl.c
@@ -1107,6 +1107,50 @@ DAXCTL_EXPORT int daxctl_dev_set_size(struct daxctl_dev *dev, unsigned long long
 	return 0;
 }
 
+DAXCTL_EXPORT int daxctl_dev_set_uuid(struct daxctl_dev *dev, uuid_t uuid)
+{
+	struct daxctl_ctx *ctx = daxctl_dev_get_ctx(dev);
+	char buf[SYSFS_ATTR_SIZE];
+	char *path = dev->dev_buf;
+	int len = dev->buf_len;
+
+	if (snprintf(path, len, "%s/uuid", dev->dev_path) >= len) {
+		err(ctx, "%s: buffer too small!\n",
+				daxctl_dev_get_devname(dev));
+		return -ENXIO;
+	}
+
+	if (uuid_is_null(uuid))
+		sprintf(buf, "0\n");
+	else
+		uuid_unparse(uuid, buf);
+
+	if (sysfs_write_attr(ctx, path, buf) < 0) {
+		err(ctx, "%s: failed to set uuid\n",
+				daxctl_dev_get_devname(dev));
+		return -ENXIO;
+	}
+
+	/*
+	 * On a sparse region the kernel populates the device size as a
+	 * side effect of claiming the matching dax_resource(s); refresh
+	 * the cached size so callers see the post-claim value.
+	 */
+	if (snprintf(path, len, "%s/size", dev->dev_path) >= len) {
+		err(ctx, "%s: buffer too small!\n",
+				daxctl_dev_get_devname(dev));
+		return -ENXIO;
+	}
+	if (sysfs_read_attr(ctx, path, buf) < 0) {
+		err(ctx, "%s: failed to read back size\n",
+				daxctl_dev_get_devname(dev));
+		return -ENXIO;
+	}
+	dev->size = strtoull(buf, NULL, 0);
+
+	return 0;
+}
+
 DAXCTL_EXPORT unsigned long daxctl_dev_get_align(struct daxctl_dev *dev)
 {
 	return dev->align;
diff --git a/daxctl/lib/libdaxctl.sym b/daxctl/lib/libdaxctl.sym
index 3098811..16792eb 100644
--- a/daxctl/lib/libdaxctl.sym
+++ b/daxctl/lib/libdaxctl.sym
@@ -104,3 +104,8 @@ LIBDAXCTL_10 {
 global:
 	daxctl_dev_is_system_ram_capable;
 } LIBDAXCTL_9;
+
+LIBDAXCTL_11 {
+global:
+	daxctl_dev_set_uuid;
+} LIBDAXCTL_10;
diff --git a/daxctl/libdaxctl.h b/daxctl/libdaxctl.h
index 53c6bbd..cdd5995 100644
--- a/daxctl/libdaxctl.h
+++ b/daxctl/libdaxctl.h
@@ -63,6 +63,7 @@ int daxctl_dev_get_minor(struct daxctl_dev *dev);
 unsigned long long daxctl_dev_get_resource(struct daxctl_dev *dev);
 unsigned long long daxctl_dev_get_size(struct daxctl_dev *dev);
 int daxctl_dev_set_size(struct daxctl_dev *dev, unsigned long long size);
+int daxctl_dev_set_uuid(struct daxctl_dev *dev, uuid_t uuid);
 unsigned long daxctl_dev_get_align(struct daxctl_dev *dev);
 int daxctl_dev_set_align(struct daxctl_dev *dev, unsigned long align);
 int daxctl_dev_set_mapping(struct daxctl_dev *dev, unsigned long long start,
-- 
2.43.0