loop: optionally use ioctl(LOOP_CONFIGURE) to set up loopdevs
LOOP_CONFIGURE is added to Linux 5.8
function old new delta
NO_LOOP_CONFIGURE (old code):
set_loop 784 782 -2
LOOP_CONFIGURE:
set_loop 784 653 -131
TRY_LOOP_CONFIGURE:
set_loop 784 811 +27
Based on a patch by Xiaoming Ni <nixiaoming@huawei.com>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/libbb/Config.src b/libbb/Config.src
index 66a3ffa..b980f19 100644
--- a/libbb/Config.src
+++ b/libbb/Config.src
@@ -369,3 +369,25 @@
For example, this means that entering 'l', 's', ' ', 0xff, [Enter]
at shell prompt will list file named 0xff (single char name
with char value 255), not file named '?'.
+
+choice
+ prompt "Use LOOP_CONFIGURE for losetup and loop mounts"
+ default TRY_LOOP_CONFIGURE
+ help
+ LOOP_CONFIGURE is added to Linux 5.8
+ https://lwn.net/Articles/820408/
+ This allows userspace to completely setup a loop device with a single
+ ioctl, removing the in-between state where the device can be partially
+ configured - eg the loop device has a backing file associated with it,
+ but is reading from the wrong offset.
+
+config LOOP_CONFIGURE
+ bool "use LOOP_CONFIGURE, needs kernel >= 5.8"
+
+config NO_LOOP_CONFIGURE
+ bool "use LOOP_SET_FD + LOOP_SET_STATUS"
+
+config TRY_LOOP_CONFIGURE
+ bool "try LOOP_CONFIGURE, fall back to LOOP_SET_FD + LOOP_SET_STATUS"
+
+endchoice