Messages in this thread | | | Date | Thu, 25 Oct 2012 19:38:30 +0400 | From | "Maxim V. Patlasov" <> | Subject | Re: [PATCH 08/11] fuse: use req->page_descs[] for argpages cases |
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Miklos,
10/25/2012 06:05 PM, Miklos Szeredi пишет: > Maxim Patlasov <mpatlasov@parallels.com> writes: > >> @@ -888,11 +888,11 @@ static int fuse_copy_pages(struct fuse_copy_state *cs, unsigned nbytes, >> { >> unsigned i; >> struct fuse_req *req = cs->req; >> - unsigned offset = req->page_descs[0].offset; >> - unsigned count = min(nbytes, (unsigned) PAGE_SIZE - offset); >> >> for (i = 0; i < req->num_pages && (nbytes || zeroing); i++) { >> int err; >> + unsigned offset = req->page_descs[i].offset; >> + unsigned count = min(nbytes, req->page_descs[i].length); > Wouldn't it be cleaner if callers calculated the last page's .length > value from the total number of bytes? So this would just be > > unsigned count = req->page_descs[i].length; > > And at the end of the function we can assert that nbytes went to exactly > zero with a WARN_ON(). > > But this is a change that needs careful testing, so maybe we're better > off having that as a separate incremental patch later...
It cannot be as simple as 'unsigned count = req->page_descs[i].length' because in case of short reads 'nbytes' (coming from userspace) can be unpredictably small. Modulo you share my opinion that a caller of fuse_copy_pages() shouldn't modify req->page_descs[i].length.
As for WARN_ON(), we could probably guarantee that 'nbytes' <= capacity(req->pages[]) in WRITEs, but in READs, 'nbytes' comes from userspace and I'm not sure it's OK to clutter logs due to misbehaved userspace fuse (if we get 'nbytes' unexpectedly large).
Thanks, Maxim -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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