[RFC PATCH] nvmet: Make blksize_shift configurable

[Richard Weinberger <richard@nod.at>]

Currently, the block size is automatically configured, and for
file-backed namespaces it is likely to be 4K.
While this is a reasonable default for modern storage, it can
cause confusion if someone wants to export a pre-created disk image
that uses a 512-byte block size.
As a result, partition parsing will fail.

So, just like we already do for the loop block device, let the user
configure the block size if they know better.

Signed-off-by: Richard Weinberger <richard@nod.at>
---
 drivers/nvme/target/configfs.c    | 30 ++++++++++++++++++++++++++++++
 drivers/nvme/target/io-cmd-bdev.c |  4 +++-
 drivers/nvme/target/io-cmd-file.c | 15 +++++++++------
 3 files changed, 42 insertions(+), 7 deletions(-)

diff --git a/drivers/nvme/target/configfs.c b/drivers/nvme/target/configfs.c
index e44ef69dffc2..2fd9cc3b1d00 100644
--- a/drivers/nvme/target/configfs.c
+++ b/drivers/nvme/target/configfs.c
@@ -797,6 +797,35 @@ static ssize_t nvmet_ns_resv_enable_store(struct config_item *item,
 }
 CONFIGFS_ATTR(nvmet_ns_, resv_enable);
 
+static ssize_t nvmet_ns_blksize_shift_show(struct config_item *item, char *page)
+{
+	return sysfs_emit(page, "%d\n", to_nvmet_ns(item)->blksize_shift);
+}
+
+static ssize_t nvmet_ns_blksize_shift_store(struct config_item *item,
+		const char *page, size_t count)
+{
+	struct nvmet_ns *ns = to_nvmet_ns(item);
+	u32 shift;
+	int ret;
+
+	ret = kstrtou32(page, 0, &shift);
+	if (ret)
+		return ret;
+
+	mutex_lock(&ns->subsys->lock);
+	if (ns->enabled) {
+		pr_err("the ns:%d is already enabled.\n", ns->nsid);
+		mutex_unlock(&ns->subsys->lock);
+		return -EINVAL;
+	}
+	ns->blksize_shift = shift;
+	mutex_unlock(&ns->subsys->lock);
+
+	return count;
+}
+CONFIGFS_ATTR(nvmet_ns_, blksize_shift);
+
 static struct configfs_attribute *nvmet_ns_attrs[] = {
 	&nvmet_ns_attr_device_path,
 	&nvmet_ns_attr_device_nguid,
@@ -806,6 +835,7 @@ static struct configfs_attribute *nvmet_ns_attrs[] = {
 	&nvmet_ns_attr_buffered_io,
 	&nvmet_ns_attr_revalidate_size,
 	&nvmet_ns_attr_resv_enable,
+	&nvmet_ns_attr_blksize_shift,
 #ifdef CONFIG_PCI_P2PDMA
 	&nvmet_ns_attr_p2pmem,
 #endif
diff --git a/drivers/nvme/target/io-cmd-bdev.c b/drivers/nvme/target/io-cmd-bdev.c
index 83be0657e6df..a86010af4670 100644
--- a/drivers/nvme/target/io-cmd-bdev.c
+++ b/drivers/nvme/target/io-cmd-bdev.c
@@ -100,7 +100,9 @@ int nvmet_bdev_ns_enable(struct nvmet_ns *ns)
 	}
 	ns->bdev = file_bdev(ns->bdev_file);
 	ns->size = bdev_nr_bytes(ns->bdev);
-	ns->blksize_shift = blksize_bits(bdev_logical_block_size(ns->bdev));
+
+	if (!ns->blksize_shift)
+		ns->blksize_shift = blksize_bits(bdev_logical_block_size(ns->bdev));
 
 	ns->pi_type = 0;
 	ns->metadata_size = 0;
diff --git a/drivers/nvme/target/io-cmd-file.c b/drivers/nvme/target/io-cmd-file.c
index 2d068439b129..5893b64179fb 100644
--- a/drivers/nvme/target/io-cmd-file.c
+++ b/drivers/nvme/target/io-cmd-file.c
@@ -49,12 +49,15 @@ int nvmet_file_ns_enable(struct nvmet_ns *ns)
 
 	nvmet_file_ns_revalidate(ns);
 
-	/*
-	 * i_blkbits can be greater than the universally accepted upper bound,
-	 * so make sure we export a sane namespace lba_shift.
-	 */
-	ns->blksize_shift = min_t(u8,
-			file_inode(ns->file)->i_blkbits, 12);
+	if (!ns->blksize_shift) {
+		/*
+		 * i_blkbits can be greater than the universally accepted
+		 * upper bound, so make sure we export a sane namespace
+		 * lba_shift.
+		 */
+		ns->blksize_shift = min_t(u8,
+				file_inode(ns->file)->i_blkbits, 12);
+	}
 
 	ns->bvec_pool = mempool_create(NVMET_MIN_MPOOL_OBJ, mempool_alloc_slab,
 			mempool_free_slab, nvmet_bvec_cache);
-- 
2.48.1