Dear maintainers of LustreFS and other experienced kernel developers!
I am working on fixing some sparse warnings as a task of Eudyptula Challenge.
There's a thing that look suspiciously to me (or I just don't
understand it). This looks same both in upstream kernel code in
drivers/staging/ and in https://github.com/Xyratex/lustre-stable.git
(it doesn't fetch from http://git.whamcloud.com/fs/lustre-release.git
but I guess it is similar with Xyratex repo).
In lnet/lnet/lib-move.c, in lnet_copy_iov2iov(), at line 209, there is
memcpy((char *)diov->iov_base + doffset,
(char *)siov->iov_base + soffset, this_nob);
diov and siov are struct iovec *, and iov_base in it is void __user *.
Are diov and siov really used semantically correctly here, holding
userspace addresses in iov_base?
Is it semantically correct to use memcpy to copy bytes from one
userspace address to another?
How to treat the comment "/* NB diov, siov are READ-ONLY */" at line
177 in the same procedure? Is it adequate?
This above-mentioned memcpy operation causes sparse warnings "warning:
cast removes address space of expression" for both first and second
line. When i change it to
memcpy((void __user *)((char __user *)diov->iov_base + doffset),
(void __user *)((char __user *)siov->iov_base
+ soffset), this_nob);
It gives other sparse warnings:
drivers/staging/lustre/lnet/lnet/lib-move.c:208:25: warning: incorrect
type in argument 1 (different address spaces)
drivers/staging/lustre/lnet/lnet/lib-move.c:208:25: expected void *to
drivers/staging/lustre/lnet/lnet/lib-move.c:208:25: got void
drivers/staging/lustre/lnet/lnet/lib-move.c:209:26: warning: incorrect
type in argument 2 (different address spaces)
drivers/staging/lustre/lnet/lnet/lib-move.c:209:26: expected void const *from
drivers/staging/lustre/lnet/lnet/lib-move.c:209:26: got void
What is supposed way to avoid warnings in this case?