David,
the possibility of unloaded module that would remove the access to
sysfs, as you point out.
Kindly note, the patch below made /dev/btrfs-control a static node,
-----
commit 578454ff7eab61d13a26b568f99a89a2c9edc881
Author: Kay Sievers <kay.sievers@xxxxxxxx>
Date: Thu May 20 18:07:20 2010 +0200
driver core: add devname module aliases to allow module on-demand
auto-loading
------
And here the function, check_or_load_btrfs_ko(), in the PATCH v2 2/5,
will take care of this problem.
--------
+
+int check_or_load_btrfs_ko()
+{
+ int fd;
+
+ /*
+ * open will load btrfs kernel module if its not loaded,
+ * and if the kernel has CONFIG auto load set?
+ */
+ fd = open("/dev/btrfs-control", O_RDONLY);
+ if (fd < 0)
+ return -errno;
+
+ close(fd);
+ return 0;
+}
+
--------
Since now static minor number for /dev/btrfs-control is mapped to
the btrfs kernel module, it will ensure btrfs is loaded when
/dev/btrfs-control is accessed.
Further, /dev/btrfs-control node is created by udevd, by reading
the modules.devname which is either supplied/updated by the distro
or compilation.
For systems without udev, IMO should run mknod ..btrfs-control
in their install script which I guess is a must.
--------
# ls -li /dev/btrfs-control
7338 crw-rw---- 1 root disk 10, 234 Dec 5 10:45 /dev/btrfs-control
# cat modules.devname | egrep btrfs
btrfs btrfs-control c10:234
# cat ./include/linux/miscdevice.h | egrep BTRFS
#define BTRFS_MINOR 234
--------
So IMO this is not a real problem.
Thanks, Anand
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