Re: [Qemu-devel] [PATCH] net: Add persistent flag to -net tap option

[Roy Vardi]

> -----Original Message-----
> From: Jason Wang [mailto:address@hidden
> Sent: Monday, December 22, 2014 8:33 AM
> To: Roy Vardi; address@hidden
> Cc: address@hidden; address@hidden; address@hidden;
> Noam Camus; address@hidden
> Subject: Re: [Qemu-devel] [PATCH] net: Add persistent flag to -net tap option
> 
> 
> On 12/21/2014 03:48 PM, Roy Vardi wrote:
> > From: Roy Vardi <address@hidden>
> >
> >     Add 'persistent' boolean flag to -net tap option.
> >     When set to off - tap interface will be released on shutdown
> >     When set to on\not specified - tap interface will remain
> 
> I'm interested of the user cases in the case. Usually, persistent flag was 
> used to
> let privileged application to create/configure the device and then it could be
> used by non-privileged users. If qemu has already had privilege, why need set
> persistent in this case?

We're running qemu as users, non-privilege... 
Our work flow includes:
1. Running an internal tool for opening a persistent tap interface 
2. Running qemu with the tap interface we got from above
Our environment includes a lot of such qemu runs, and we want to avoid "zombie" 
tap interfaces, and we achieve it with this new flag I've added.
It's also worth mentioning that we're able to configure the tap interface in 
qemu through the ioctl as users (non-privileged).
If the persistent flag is not given (or if it's given as on), I'm not actively 
doing anything, the same code that you're familiar with will run. My change 
only affects the case where "persistent=off" is given

> >     Running with -net tap,persistent=off will force the tap interface
> >     down when qemu goes down, thus ensuring that there're no zombie tap
> >     interfaces left
> >
> >     This is achieved using another ioctl
> >
> >     Note: This commit includes the above support only for linux
> > systems
> 
> But your patch will break non-linux builds, no?

I'm using qemu only on linux, so I can't really tell.
I would appreciate it if you could perhaps tell me how can I make sure I didn't 
break anything 

> >
> > Signed-off-by: Roy Vardi <address@hidden>
> > ---
> >  net/tap-linux.c  |   14 +++++++++++++-
> >  net/tap.c        |   10 ++++++----
> >  net/tap_int.h    |    2 +-
> >  qapi-schema.json |    5 ++++-
> >  qemu-options.hx  |    3 ++-
> >  5 files changed, 26 insertions(+), 8 deletions(-)
> >
> > diff --git a/net/tap-linux.c b/net/tap-linux.c index 812bf2d..7a98390
> > 100644
> > --- a/net/tap-linux.c
> > +++ b/net/tap-linux.c
> > @@ -29,6 +29,7 @@
> >
> >  #include <net/if.h>
> >  #include <sys/ioctl.h>
> > +#include <linux/if_tun.h>
> 
> To reduce headers dependency, we put tun flags in net/tap-linux.h.

Sure, I'll fix and will send another patch

> >
> >  #include "sysemu/sysemu.h"
> >  #include "qemu-common.h"
> > @@ -37,7 +38,7 @@
> >  #define PATH_NET_TUN "/dev/net/tun"
> >
> >  int tap_open(char *ifname, int ifname_size, int *vnet_hdr,
> > -             int vnet_hdr_required, int mq_required)
> > +             int vnet_hdr_required, int mq_required, int
> > + persistent_required)
> >  {
> >      struct ifreq ifr;
> >      int fd, ret;
> > @@ -109,6 +110,17 @@ int tap_open(char *ifname, int ifname_size, int
> *vnet_hdr,
> >          close(fd);
> >          return -1;
> >      }
> > +
> > +    if (!persistent_required) {
> > +        ret = ioctl(fd, TUNSETPERSIST, 0);
> > +        if (ret != 0) {
> > +            error_report("could not configure non-persistent %s (%s): %m",
> > +                        PATH_NET_TUN, ifr.ifr_name);
> > +            close(fd);
> > +            return -1;
> > +        }
> > +    }
> > +
> >      pstrcpy(ifname, ifname_size, ifr.ifr_name);
> >      fcntl(fd, F_SETFL, O_NONBLOCK);
> >      return fd;
> > diff --git a/net/tap.c b/net/tap.c
> > index bde6b58..055863a 100644
> > --- a/net/tap.c
> > +++ b/net/tap.c
> > @@ -556,7 +556,8 @@ int net_init_bridge(const NetClientOptions *opts,
> > const char *name,
> >
> >  static int net_tap_init(const NetdevTapOptions *tap, int *vnet_hdr,
> >                          const char *setup_script, char *ifname,
> > -                        size_t ifname_sz, int mq_required)
> > +                        size_t ifname_sz, int mq_required,
> > +                        int persistent_required)
> >  {
> >      int fd, vnet_hdr_required;
> >
> > @@ -569,7 +570,7 @@ static int net_tap_init(const NetdevTapOptions *tap,
> int *vnet_hdr,
> >      }
> >
> >      TFR(fd = tap_open(ifname, ifname_sz, vnet_hdr, vnet_hdr_required,
> > -                      mq_required));
> > +                      mq_required, persistent_required));
> >      if (fd < 0) {
> >          return -1;
> >      }
> > @@ -688,7 +689,7 @@ int net_init_tap(const NetClientOptions *opts, const
> char *name,
> >                   NetClientState *peer)  {
> >      const NetdevTapOptions *tap;
> > -    int fd, vnet_hdr = 0, i = 0, queues;
> > +    int fd, vnet_hdr = 0, i = 0, queues, persistent;
> >      /* for the no-fd, no-helper case */
> >      const char *script = NULL; /* suppress wrong "uninit'd use" gcc 
> > warning */
> >      const char *downscript = NULL;
> > @@ -699,6 +700,7 @@ int net_init_tap(const NetClientOptions *opts, const
> char *name,
> >      tap = opts->tap;
> >      queues = tap->has_queues ? tap->queues : 1;
> >      vhostfdname = tap->has_vhostfd ? tap->vhostfd : NULL;
> > +    persistent = tap->has_persistent ? tap->persistent : 1;
> >
> >      /* QEMU vlans does not support multiqueue tap, in this case peer is 
> > set.
> >       * For -netdev, peer is always NULL. */ @@ -816,7 +818,7 @@ int
> > net_init_tap(const NetClientOptions *opts, const char *name,
> >
> >          for (i = 0; i < queues; i++) {
> >              fd = net_tap_init(tap, &vnet_hdr, i >= 1 ? "no" : script,
> > -                              ifname, sizeof ifname, queues > 1);
> > +                              ifname, sizeof ifname, queues > 1,
> > + persistent);
> >              if (fd == -1) {
> >                  return -1;
> >              }
> > diff --git a/net/tap_int.h b/net/tap_int.h index 79afdf2..0eb2168
> > 100644
> > --- a/net/tap_int.h
> > +++ b/net/tap_int.h
> > @@ -30,7 +30,7 @@
> >  #include "qapi-types.h"
> >
> >  int tap_open(char *ifname, int ifname_size, int *vnet_hdr,
> > -             int vnet_hdr_required, int mq_required);
> > +             int vnet_hdr_required, int mq_required, int
> > + persistent_required);
> >
> >  ssize_t tap_read_packet(int tapfd, uint8_t *buf, int maxlen);
> >
> > diff --git a/qapi-schema.json b/qapi-schema.json index
> > 563b4ad..99e6482 100644
> > --- a/qapi-schema.json
> > +++ b/qapi-schema.json
> > @@ -2007,6 +2007,8 @@
> >  #
> >  # @queues: #optional number of queues to be created for multiqueue
> > capable tap  #
> > +# @persistent: #optional for opening tap in persistent mode (default:
> > +on) (Since: 2.3) #
> >  # Since 1.2
> >  ##
> >  { 'type': 'NetdevTapOptions',
> > @@ -2023,7 +2025,8 @@
> >      '*vhostfd':    'str',
> >      '*vhostfds':   'str',
> >      '*vhostforce': 'bool',
> > -    '*queues':     'uint32'} }
> > +    '*queues':     'uint32',
> > +    '*persistent': 'bool'} }
> >
> >  ##
> >  # @NetdevSocketOptions
> > diff --git a/qemu-options.hx b/qemu-options.hx index 10b9568..d8c033d
> > 100644
> > --- a/qemu-options.hx
> > +++ b/qemu-options.hx
> > @@ -1417,7 +1417,7 @@ DEF("net", HAS_ARG, QEMU_OPTION_net,
> >      "-net tap[,vlan=n][,name=str],ifname=name\n"
> >      "                connect the host TAP network interface to VLAN 'n'\n"
> >  #else
> > -    "-net
> tap[,vlan=n][,name=str][,fd=h][,fds=x:y:...:z][,ifname=name][,script=file][,down
> script=dfile][,helper=helper][,sndbuf=nbytes][,vnet_hdr=on|off][,vhost=on|off
> ][,vhostfd=h][,vhostfds=x:y:...:z][,vhostforce=on|off][,queues=n]\n"
> > +    "-net
> tap[,vlan=n][,name=str][,fd=h][,fds=x:y:...:z][,ifname=name][,script=file][,down
> script=dfile][,helper=helper][,sndbuf=nbytes][,vnet_hdr=on|off][,vhost=on|off
> ][,vhostfd=h][,vhostfds=x:y:...:z][,vhostforce=on|off][,queues=n][,persistent=o
> n|off]\n"
> >      "                connect the host TAP network interface to VLAN 'n'\n"
> >      "                use network scripts 'file' (default=" 
> > DEFAULT_NETWORK_SCRIPT
> ")\n"
> >      "                to configure it and 'dfile' (default="
> DEFAULT_NETWORK_DOWN_SCRIPT ")\n"
> > @@ -1437,6 +1437,7 @@ DEF("net", HAS_ARG, QEMU_OPTION_net,
> >      "                use 'vhostfd=h' to connect to an already opened vhost 
> > net
> device\n"
> >      "                use 'vhostfds=x:y:...:z to connect to multiple 
> > already opened vhost
> net devices\n"
> >      "                use 'queues=n' to specify the number of queues to be 
> > created for
> multiqueue TAP\n"
> > +    "                use 'persistent=off' to release the TAP interface on 
> > shutdown
> (default=on)\n"
> 
> As Stefan mentioned, we don't set persistent by default in the past. So please
> don't change this behaviour.

I didn't change any legacy behavior.
If the persistent flag is not given, then the code that will be executed is as 
it is today.
I'm only actively changing (configuring) the interface if "persistent=off" is 
given

> >      "-net bridge[,vlan=n][,name=str][,br=bridge][,helper=helper]\n"
> >      "                connects a host TAP network interface to a host 
> > bridge device
> 'br'\n"
> >      "                (default=" DEFAULT_BRIDGE_INTERFACE ") using the 
> > program
> 'helper'\n"