Hello all,
I was writing a device mapper target.
Now in that target for each bio request I set the bi_end_io field to
my endio function "my_end_io".
So that whenever the bio request gets complete it will call the
"my_end_io" function.
While registering the device mapper target we provide a structure
called "target_type" to the device mapper.
This structure is like this.
static struct target_type my_dm_target = {
.name = "my_dmt",
.version = {1, 0, 0},
.module = THIS_MODULE,
.ctr = dmt_ctr,
.dtr = dmt_dtr,
.map = dmt_map,
.end_io = dmt_endio,
};
It contains many other fields(Mainly function pointers).
Now if you have observed the end_io field in the target_type, this is function.
I was not able to figure out why there is another end_io filed is
given if we can set the bi_end_io field in each bio(my_end_io).
I was also not getting what's the purpose of the end_io function given
in the target_type. And when this function gets called.
Earlier I did not define end_io function (from target_type ) but
because of that OOPS was generated. Later I dug the logs, I found that
clone_endio function in dm.c is trying to access the end_io field from
the target_type structure. But since function was not defined the
end_io field was NULL. So it gives OOPS NULL pointer reference at that
point.
Looking forward for some help.....
Regards,
Gaurav
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