A read-only block device must currently be flagged as such when
configuring the iblock backstore, via a readonly=1 configfs parameter.
If a read-only block device is used without explicitly providing the
parameter, then backstore enablement fails with EACCES, e.g.
losetup --read-only /dev/loop0 /lofile
mkdir -p /sys/kernel/config/target/core/iblock_0/loopy
echo "udev_path=/dev/loop0" \
> /sys/kernel/config/target/core/iblock_0/loopy/control
echo "1" > /sys/kernel/config/target/core/iblock_0/loopy/enable
sh: echo: write error: Permission denied
This change allows an iblock backstore to be demoted to read-only if the
underlying device is detected as such, via a -EACCES return value from
blkdev_get_by_path(udev_path=$readonly_device, mode & FMODE_WRITE, ...).
Signed-off-by: David Disseldorp <ddiss@xxxxxxx>
---
drivers/target/target_core_iblock.c | 12 ++++++++++++
1 file changed, 12 insertions(+)
diff --git a/drivers/target/target_core_iblock.c b/drivers/target/target_core_iblock.c
index 07c814c42648..cafba262a440 100644
--- a/drivers/target/target_core_iblock.c
+++ b/drivers/target/target_core_iblock.c
@@ -103,6 +103,7 @@ static int iblock_configure_device(struct se_device *dev)
pr_debug( "IBLOCK: Claiming struct block_device: %s\n",
ib_dev->ibd_udev_path);
+ro_fallback:
mode = FMODE_READ|FMODE_EXCL;
if (!ib_dev->ibd_readonly)
mode |= FMODE_WRITE;
@@ -112,6 +113,17 @@ static int iblock_configure_device(struct se_device *dev)
bd = blkdev_get_by_path(ib_dev->ibd_udev_path, mode, ib_dev);
if (IS_ERR(bd)) {
ret = PTR_ERR(bd);
+ if (!ib_dev->ibd_readonly && (ret == -EACCES)) {
+ /*
+ * EACCES is returned if FMODE_WRITE is set while
+ * getting a read-only block device. Try once again
+ * without FMODE_WRITE to allow for configuration of a
+ * read-only block device without an explicit readonly=1
+ * configfs parameter in iblock_set_configfs_dev_params().
+ */
+ ib_dev->ibd_readonly = 1;
+ goto ro_fallback;
+ }
goto out_free_bioset;
}
ib_dev->ibd_bd = bd;
--
2.13.6
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