linux-kernel - Re: [PATCH] um: add a generic "fd" vector transport

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Message-ID: <c0e66bcd-7c13-31db-f347-1a3e9fac2b79@cambridgegreys.com>
Date:   Wed, 8 Apr 2020 19:10:15 +0100
From:   Anton Ivanov <anton.ivanov@...bridgegreys.com>
To:     Marc-André Lureau <marcandre.lureau@...hat.com>
Cc:     linux-um <linux-um@...ts.infradead.org>,
        joerd.simons@...labora.co.uk, richard@....at, jdike@...toit.com,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        alex.dewar@....co.uk
Subject: Re: [PATCH] um: add a generic "fd" vector transport

On 08/04/2020 18:07, Marc-André Lureau wrote:
> Hi
> 
> On Tue, Apr 7, 2020 at 11:02 PM Anton Ivanov
> <anton.ivanov@...bridgegreys.com> wrote:
>>
>> On 07/04/2020 21:28, Marc-André Lureau wrote:
>>> Learn to take a pre-opened file-descriptor for vector IO.
>>>
>>> Instead of teaching the driver to open a FD in multiple ways, it can
>>> rely on management layer to do it on its behalf. For example, this
>>> allows inheriting a preconfigured device fd or a simple socketpair()
>>> setup, without further arguments, privileges or system access by UML.
>>>
>>> Signed-off-by: Marc-André Lureau <marcandre.lureau@...hat.com>
>>> ---
>>>    arch/um/drivers/vector_user.c | 59 +++++++++++++++++++++++++++++++++++
>>>    1 file changed, 59 insertions(+)
>>>
>>> diff --git a/arch/um/drivers/vector_user.c b/arch/um/drivers/vector_user.c
>>> index 29fae0456ade..45c1550dbb37 100644
>>> --- a/arch/um/drivers/vector_user.c
>>> +++ b/arch/um/drivers/vector_user.c
>>> @@ -29,6 +29,7 @@
>>>    #include <netdb.h>
>>>    #include <stdlib.h>
>>>    #include <os.h>
>>> +#include <limits.h>
>>>    #include <um_malloc.h>
>>>    #include "vector_user.h"
>>>
>>> @@ -42,6 +43,9 @@
>>>    #define TRANS_RAW "raw"
>>>    #define TRANS_RAW_LEN strlen(TRANS_RAW)
>>>
>>> +#define TRANS_FD "fd"
>>> +#define TRANS_FD_LEN strlen(TRANS_FD)
>>> +
>>>    #define VNET_HDR_FAIL "could not enable vnet headers on fd %d"
>>>    #define TUN_GET_F_FAIL "tapraw: TUNGETFEATURES failed: %s"
>>>    #define L2TPV3_BIND_FAIL "l2tpv3_open : could not bind socket err=%i"
>>> @@ -347,6 +351,59 @@ static struct vector_fds *user_init_unix_fds(struct arglist *ifspec, int id)
>>>        return NULL;
>>>    }
>>>
>>> +static int strtofd(const char *nptr)
>>> +{
>>> +     long fd;
>>> +     char *endptr;
>>> +
>>> +     if (nptr == NULL)
>>> +             return -1;
>>> +
>>> +     errno = 0;
>>> +     fd = strtol(nptr, &endptr, 10);
>>> +     if (nptr == endptr ||
>>> +             errno != 0 ||
>>> +             *endptr != '\0' ||
>>> +             fd < 0 ||
>>> +             fd > INT_MAX) {
>>> +             return -1;
>>> +     }
>>> +     return fd;
>>> +}
>>> +
>>> +static struct vector_fds *user_init_fd_fds(struct arglist *ifspec)
>>> +{
>>> +     int fd = -1;
>>> +     char *fdarg = NULL;
>>> +     struct vector_fds *result = NULL;
>>> +
>>> +     fdarg = uml_vector_fetch_arg(ifspec, "fd");
>>> +     fd = strtofd(fdarg);
>>> +     if (fd == -1) {
>>> +             printk(UM_KERN_ERR "fd open: bad or missing fd argument");
>>> +             goto fd_cleanup;
>>> +     }
>>> +
>>> +     result = uml_kmalloc(sizeof(struct vector_fds), UM_GFP_KERNEL);
>>> +     if (result == NULL) {
>>> +             printk(UM_KERN_ERR "fd open: allocation failed");
>>> +             goto fd_cleanup;
>>> +     }
>>> +
>>> +     result->rx_fd = fd;
>>> +     result->tx_fd = fd;
>>> +     result->remote_addr_size = 0;
>>> +     result->remote_addr = NULL;
>>> +     return result;
>>> +
>>> +fd_cleanup:
>>> +     if (fd >= 0)
>>> +             os_close_file(fd);
>>> +     if (result != NULL)
>>> +             kfree(result);
>>> +     return NULL;
>>> +}
>>> +
>>>    static struct vector_fds *user_init_raw_fds(struct arglist *ifspec)
>>>    {
>>>        int rxfd = -1, txfd = -1;
>>> @@ -578,6 +635,8 @@ struct vector_fds *uml_vector_user_open(
>>>                return user_init_socket_fds(parsed, ID_L2TPV3);
>>>        if (strncmp(transport, TRANS_BESS, TRANS_BESS_LEN) == 0)
>>>                return user_init_unix_fds(parsed, ID_BESS);
>>> +     if (strncmp(transport, TRANS_FD, TRANS_FD_LEN) == 0)
>>> +             return user_init_fd_fds(parsed);
>>>        return NULL;
>>>    }
>>>
>>>
>>
>> We should also control enable/disable of recv/sendmmsg as an option here.
>>
>> It can be made generic and be fed into get_transport_options() in
>> vector_kern.c as an override.
> 
> So actually, there seems to be a way to do that already:
> 
> vec0:transport=fd,fd=N,vec=0

I have forgotten about it (it's been a while since I wrote the drivers).

I will update the docs.

In that case the patch looks good to go, I will ack it shortly.

> 
>>
>> --
>> Anton R. Ivanov
>> Cambridgegreys Limited. Registered in England. Company Number 10273661
>> https://www.cambridgegreys.com/
>>
> 
> 


-- 
Anton R. Ivanov
Cambridgegreys Limited. Registered in England. Company Number 10273661
https://www.cambridgegreys.com/