qstr abuse in git-cifs

qstr abuse in git-cifs

[Andrew Morton]

static int cifs_ci_compare(struct dentry *dentry, struct qstr *a,
                           struct qstr *b)
{
        struct nls_table *codepage = CIFS_SB(dentry->d_inode->i_sb)->local_nls;

        if ((a->len == b->len) &&
            (nls_strnicmp(codepage, a->name, b->name, a->len) == 0)) {
                /*
                 * To preserve case, don't let an existing negative dentry's
                 * case take precedence.  If a is not a negative dentry, this
                 * should have no side effects
                 */
                memcpy(a->name, b->name, a->len);
                return 0;
        }
        return 1;
}

produces

fs/cifs/dir.c: In function 'cifs_ci_compare':
fs/cifs/dir.c:596: warning: passing argument 1 of '__constant_memcpy' discards qualifiers from pointer target type
fs/cifs/dir.c:596: warning: passing argument 1 of '__memcpy' discards qualifiers from pointer target type

I suspect that bad things are happening in there.

It's strange for a "comparison" function to go and alter one of the things
which it's comparing, too.

Re: qstr abuse in git-cifs

[Steve French]

> I suspect that bad things are happening in there
I doubt that it is too bad since various filesystems (including JFS
and CIFS) have always written over qstr->name in these dentries in
order to better handle case insensitive compares.   Other than trying
to remove the compiler warning recently (mainline throws the same
warning), I didn't see what changed other than now displaying a
warning.   I agree that it looks strange, but I also don't see a
trivial way to change it.  Any ideas on how to prevent the case of an
existing negative dentry from taking precedence? Creating more
dentries for these duplicates would seem like a worse idea.

> fs/cifs/dir.c: In function 'cifs_ci_compare':
> fs/cifs/dir.c:596: warning: passing argument 1 of '__constant_memcpy' discards qualifiers from pointer target type
> fs/cifs/dir.c:596: warning: passing argument 1 of '__memcpy' discards qualifiers from pointer target type

-- 
Thanks,

Steve