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From: Long Li <longli@microsoft.com>
To: ronnie sahlberg <ronniesahlberg@gmail.com>
Cc: Steve French <sfrench@samba.org>,
	linux-cifs <linux-cifs@vger.kernel.org>,
	"samba-technical@lists.samba.org"
	<samba-technical@lists.samba.org>,
	LKML <linux-kernel@vger.kernel.org>,
	"longli@linuxonhyperv.com" <longli@linuxonhyperv.com>
Subject: RE: [PATCH] cifs: smbd: Calculate the correct maximum packet size for segmented SMBDirect send/receive
Date: Thu, 26 Mar 2020 02:43:29 +0000
Message-ID: <BN8PR21MB1155CECE3C53742CC389E5F9CECF0@BN8PR21MB1155.namprd21.prod.outlook.com> (raw)
In-Reply-To: <CAN05THTH8-pK9uw77COWSUQ_knztT1o1Ms0b=2PPvmBJd=ovUw@mail.gmail.com>

>Subject: Re: [PATCH] cifs: smbd: Calculate the correct maximum packet size
>for segmented SMBDirect send/receive
>
>Long Li,
>
>Mostly looks good  but the magic constant 49 I think is wrong.
>49 is the structure size of the read/write request header but for these sizes, if
>they are odd it just means that the header contain a variable sized blob.
>I.e. the size is 48 bytes (for the fixed part of the header) + a variable part
>which in this case are the ChannelInfo blobs.

Agreed. Using a magic number is not a good idea.

I was looking at request size definitions in 
"fs/cifs/smb2pdu.c",  they are defined at
static const int smb2_req_struct_sizes[NUMBER_OF_SMB2_COMMANDS]

for read and write, the sizes are:
        /* SMB2_READ */ 49,
        /* SMB2_WRITE */ 49,

They are used to calculate command header sizes, and fill in the request headers. Maybe I should use this variable to get the size?

>
>So we should probably add to smb2pdu.h a #define
>MAX_SMB2_READWRITE_RESPONSE_SIZE 48 and use this in the calculations.
>Then we need to add the maximum size we will use for ChannelInfo.
>
>Maybe we should have a define also for the
>MAX_SMB2_CHANNEL_INFO_SIZE
>
>regards
>ronnie sahlberg
>
>On Thu, Mar 26, 2020 at 5:31 AM longli--- via samba-technical <samba-
>technical@lists.samba.org> wrote:
>>
>> From: Long Li <longli@microsoft.com>
>>
>> The packet size needs to take account of SMB2 header size and possible
>> encryption header size. This is only done when signing is used and it
>> is for RDMA send/receive, not read/write.
>>
>> Also remove the dead SMBD code in smb2_negotiate_r(w)size.
>>
>> Signed-off-by: Long Li <longli@microsoft.com>
>> ---
>>  fs/cifs/smb2ops.c   | 38 ++++++++++++++++----------------------
>>  fs/cifs/smbdirect.c |  3 +--
>>  2 files changed, 17 insertions(+), 24 deletions(-)
>>
>> diff --git a/fs/cifs/smb2ops.c b/fs/cifs/smb2ops.c index
>> 4c0922596467..9043d34eef43 100644
>> --- a/fs/cifs/smb2ops.c
>> +++ b/fs/cifs/smb2ops.c
>> @@ -332,16 +332,6 @@ smb2_negotiate_wsize(struct cifs_tcon *tcon,
>struct smb_vol *volume_info)
>>         /* start with specified wsize, or default */
>>         wsize = volume_info->wsize ? volume_info->wsize :
>CIFS_DEFAULT_IOSIZE;
>>         wsize = min_t(unsigned int, wsize, server->max_write); -#ifdef
>> CONFIG_CIFS_SMB_DIRECT
>> -       if (server->rdma) {
>> -               if (server->sign)
>> -                       wsize = min_t(unsigned int,
>> -                               wsize, server->smbd_conn->max_fragmented_send_size);
>> -               else
>> -                       wsize = min_t(unsigned int,
>> -                               wsize, server->smbd_conn->max_readwrite_size);
>> -       }
>> -#endif
>>         if (!(server->capabilities & SMB2_GLOBAL_CAP_LARGE_MTU))
>>                 wsize = min_t(unsigned int, wsize,
>> SMB2_MAX_BUFFER_SIZE);
>>
>> @@ -360,8 +350,15 @@ smb3_negotiate_wsize(struct cifs_tcon *tcon,
>> struct smb_vol *volume_info)  #ifdef CONFIG_CIFS_SMB_DIRECT
>>         if (server->rdma) {
>>                 if (server->sign)
>> +                       /*
>> +                        * Account for SMB2 data transfer packet header
>> +                        * SMB2_READ/SMB2_WRITE (49) and possible encryption
>> +                        * headers
>> +                        */
>>                         wsize = min_t(unsigned int,
>> -                               wsize, server->smbd_conn->max_fragmented_send_size);
>> +                               wsize,
>> +                               server->smbd_conn->max_fragmented_send_size -
>> +                                       49 - sizeof(struct
>> + smb2_transform_hdr));
>>                 else
>>                         wsize = min_t(unsigned int,
>>                                 wsize,
>> server->smbd_conn->max_readwrite_size);
>> @@ -382,16 +379,6 @@ smb2_negotiate_rsize(struct cifs_tcon *tcon, struct
>smb_vol *volume_info)
>>         /* start with specified rsize, or default */
>>         rsize = volume_info->rsize ? volume_info->rsize : CIFS_DEFAULT_IOSIZE;
>>         rsize = min_t(unsigned int, rsize, server->max_read); -#ifdef
>> CONFIG_CIFS_SMB_DIRECT
>> -       if (server->rdma) {
>> -               if (server->sign)
>> -                       rsize = min_t(unsigned int,
>> -                               rsize, server->smbd_conn->max_fragmented_recv_size);
>> -               else
>> -                       rsize = min_t(unsigned int,
>> -                               rsize, server->smbd_conn->max_readwrite_size);
>> -       }
>> -#endif
>>
>>         if (!(server->capabilities & SMB2_GLOBAL_CAP_LARGE_MTU))
>>                 rsize = min_t(unsigned int, rsize,
>> SMB2_MAX_BUFFER_SIZE); @@ -411,8 +398,15 @@
>> smb3_negotiate_rsize(struct cifs_tcon *tcon, struct smb_vol *volume_info)
>#ifdef CONFIG_CIFS_SMB_DIRECT
>>         if (server->rdma) {
>>                 if (server->sign)
>> +                       /*
>> +                        * Account for SMB2 data transfer packet header
>> +                        * SMB2_READ/SMB2_WRITE (49) and possible encryption
>> +                        * headers
>> +                        */
>>                         rsize = min_t(unsigned int,
>> -                               rsize, server->smbd_conn->max_fragmented_recv_size);
>> +                               rsize,
>> +                               server->smbd_conn->max_fragmented_recv_size -
>> +                                       49 - sizeof(struct
>> + smb2_transform_hdr));
>>                 else
>>                         rsize = min_t(unsigned int,
>>                                 rsize,
>> server->smbd_conn->max_readwrite_size);
>> diff --git a/fs/cifs/smbdirect.c b/fs/cifs/smbdirect.c index
>> eb1e40af9f3a..0327b575ab87 100644
>> --- a/fs/cifs/smbdirect.c
>> +++ b/fs/cifs/smbdirect.c
>> @@ -2097,8 +2097,7 @@ int smbd_send(struct TCP_Server_Info *server,
>>         for (i = 0; i < num_rqst; i++)
>>                 remaining_data_length += smb_rqst_len(server,
>> &rqst_array[i]);
>>
>> -       if (remaining_data_length + sizeof(struct smbd_data_transfer) >
>> -               info->max_fragmented_send_size) {
>> +       if (remaining_data_length > info->max_fragmented_send_size) {
>>                 log_write(ERR, "payload size %d > max size %d\n",
>>                         remaining_data_length, info->max_fragmented_send_size);
>>                 rc = -EINVAL;
>> --
>> 2.17.1
>>
>>

  reply index

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-03-25 19:30 longli
2020-03-26  2:02 ` ronnie sahlberg
2020-03-26  2:43   ` Long Li [this message]
2020-03-26  3:03     ` ronnie sahlberg
2020-03-26  3:08       ` Long Li

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