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Date: Wed, 5 Feb 2020 08:35:04 +0100
From: Dominique Martinet <asmadeus@...ewreck.org>
To: Sergey Alirzaev <l29ah@...k.li>
Cc: v9fs-developer@...ts.sourceforge.net,
Eric Van Hensbergen <ericvh@...il.com>,
Latchesar Ionkov <lucho@...kov.net>,
"David S. Miller" <davem@...emloft.net>,
Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] 9pnet: allow making incomplete read requests
Sergey Alirzaev wrote on Wed, Feb 05, 2020:
> A user doesn't necessarily want to wait for all the requested data to
> be available, since the waiting time is unbounded.
I'm not sure I agree on the argument there: the waiting time is
unbounded for a single request as well. What's your use case?
I think it would be better to describe what you really do with
O_NONBLOCK that requires this, and not just false theoritical
arguments.
> Signed-off-by: Sergey Alirzaev <l29ah@...k.li>
Code-wise looks mostly good, just a nitpick about keeping the total
variable in p9_client_read_once inline.
> ---
> include/net/9p/client.h | 2 +
> net/9p/client.c | 133 ++++++++++++++++++++++------------------
> 2 files changed, 76 insertions(+), 59 deletions(-)
>
> --- a/net/9p/client.c
> +++ b/net/9p/client.c
> @@ -1548,83 +1548,98 @@ EXPORT_SYMBOL(p9_client_unlinkat);
>
> int
> p9_client_read(struct p9_fid *fid, u64 offset, struct iov_iter *to, int *err)
> +{
> + int total = 0;
> + *err = 0;
> +
> + while (iov_iter_count(to)) {
> + int count;
> +
> + count = p9_client_read_once(fid, offset, to, err);
> + if (!count || *err)
> + break;
> + offset += count;
> + total += count;
> + }
> + return total;
> +}
> +EXPORT_SYMBOL(p9_client_read);
> +
> +int
> +p9_client_read_once(struct p9_fid *fid, u64 offset, struct iov_iter *to,
> + int *err)
> {
> struct p9_client *clnt = fid->clnt;
> struct p9_req_t *req;
> int total = 0;
total only makes sense in an iterating p9_client_read, I think it makes
code harder to read here (can basically use count or 0 directly now)
> - *err = 0;
> + int count = iov_iter_count(to);
> + int rsize, non_zc = 0;
> + char *dataptr;
>
> + *err = 0;
> p9_debug(P9_DEBUG_9P, ">>> TREAD fid %d offset %llu %d\n",
> fid->fid, (unsigned long long) offset, (int)iov_iter_count(to));
>
> - while (iov_iter_count(to)) {
> - int count = iov_iter_count(to);
> - int rsize, non_zc = 0;
> - char *dataptr;
> + rsize = fid->iounit;
> + if (!rsize || rsize > clnt->msize - P9_IOHDRSZ)
> + rsize = clnt->msize - P9_IOHDRSZ;
>
> - rsize = fid->iounit;
> - if (!rsize || rsize > clnt->msize-P9_IOHDRSZ)
> - rsize = clnt->msize - P9_IOHDRSZ;
> + if (count < rsize)
> + rsize = count;
>
> - if (count < rsize)
> - rsize = count;
> + /* Don't bother zerocopy for small IO (< 1024) */
> + if (clnt->trans_mod->zc_request && rsize > 1024) {
> + /* response header len is 11
> + * PDU Header(7) + IO Size (4)
> + */
> + req = p9_client_zc_rpc(clnt, P9_TREAD, to, NULL, rsize,
> + 0, 11, "dqd", fid->fid,
> + offset, rsize);
> + } else {
> + non_zc = 1;
> + req = p9_client_rpc(clnt, P9_TREAD, "dqd", fid->fid, offset,
> + rsize);
> + }
> + if (IS_ERR(req)) {
> + *err = PTR_ERR(req);
> + return total;
> + }
>
> - /* Don't bother zerocopy for small IO (< 1024) */
> - if (clnt->trans_mod->zc_request && rsize > 1024) {
> - /*
> - * response header len is 11
> - * PDU Header(7) + IO Size (4)
> - */
> - req = p9_client_zc_rpc(clnt, P9_TREAD, to, NULL, rsize,
> - 0, 11, "dqd", fid->fid,
> - offset, rsize);
> - } else {
> - non_zc = 1;
> - req = p9_client_rpc(clnt, P9_TREAD, "dqd", fid->fid, offset,
> - rsize);
> - }
> - if (IS_ERR(req)) {
> - *err = PTR_ERR(req);
> - break;
> - }
> + *err = p9pdu_readf(&req->rc, clnt->proto_version,
> + "D", &count, &dataptr);
> + if (*err) {
> + trace_9p_protocol_dump(clnt, &req->rc);
> + p9_tag_remove(clnt, req);
> + return total;
> + }
> + if (rsize < count) {
> + pr_err("bogus RREAD count (%d > %d)\n", count, rsize);
> + count = rsize;
> + }
>
> - *err = p9pdu_readf(&req->rc, clnt->proto_version,
> - "D", &count, &dataptr);
> - if (*err) {
> - trace_9p_protocol_dump(clnt, &req->rc);
> - p9_tag_remove(clnt, req);
> - break;
> - }
> - if (rsize < count) {
> - pr_err("bogus RREAD count (%d > %d)\n", count, rsize);
> - count = rsize;
> - }
> + p9_debug(P9_DEBUG_9P, "<<< RREAD count %d\n", count);
> + if (!count) {
> + p9_tag_remove(clnt, req);
> + return total;
> + }
>
> - p9_debug(P9_DEBUG_9P, "<<< RREAD count %d\n", count);
> - if (!count) {
> - p9_tag_remove(clnt, req);
> - break;
> - }
> + if (non_zc) {
> + int n = copy_to_iter(dataptr, count, to);
>
> - if (non_zc) {
> - int n = copy_to_iter(dataptr, count, to);
> - total += n;
> - offset += n;
> - if (n != count) {
> - *err = -EFAULT;
> - p9_tag_remove(clnt, req);
> - break;
> - }
> - } else {
> - iov_iter_advance(to, count);
> - total += count;
> - offset += count;
> + total += n;
> + if (n != count) {
> + *err = -EFAULT;
> + p9_tag_remove(clnt, req);
> + return total;
> }
> - p9_tag_remove(clnt, req);
> + } else {
> + iov_iter_advance(to, count);
> + total += count;
> }
> + p9_tag_remove(clnt, req);
> return total;
> }
> -EXPORT_SYMBOL(p9_client_read);
> +EXPORT_SYMBOL(p9_client_read_once);
>
> int
> p9_client_write(struct p9_fid *fid, u64 offset, struct iov_iter *from, int *err)
--
Dominique
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