Re: [dpdk-dev] [PATCH v3 2/8] devargs: introduce removal function

["Gaëtan Rivet" <gaetan.rivet@6wind.com>]

On Wed, Jul 12, 2017 at 04:27:34AM -0400, Jan Blunck wrote:
> On Tue, Jul 11, 2017 at 7:25 PM, Gaetan Rivet <gaetan.rivet@6wind.com> wrote:
> > Hotplug support introduces the possibility of removing devices from the
> > system. Allocated resources must be freed.
> >
> > Extend the rte_devargs API to allow freeing allocated resources.
> >
> > This API is experimental and bound to change. It is currently designed
> > as a symetrical to rte_eal_devargs_add(), but the latter will evolve
> > shortly anyway.
> >
> > Its DEVTYPE parameter is currently only used to specify scan policies,
> > and those will evolve in the next release. This evolution should
> > rationalize the rte_devargs API.
> >
> > As such, the proposed API here is not the most convenient, but is
> > taylored to follow the current design and integrate easily with its main
> > use within rte_eal_hotplug_* functions.
> 
> I don't think that this is safe to do. The rte_device is using a
> reference to the allocated rte_devargs so before we remove it we need
> to make sure that the device is gone.
> 

I think you're right. No bus should need to use the rte_devargs to
remove a device, but we cannot be sure.

> Besides that the comment says that its current user is inside the EAL
> so I wonder why it is exported.
> 

I agree that there isn't much use outside. However, the converse
rte_eal_devargs_add is exposed so it makes sense to also offer the
possibility of removing one.

But it will all change with the deprecation of rte_eal_devargs_add
anyway, so let's not expose it if there is no need.

> > Signed-off-by: Gaetan Rivet <gaetan.rivet@6wind.com>
> > ---
> >  lib/librte_eal/bsdapp/eal/rte_eal_version.map   |  1 +
> >  lib/librte_eal/common/eal_common_devargs.c      | 19 +++++++++++++++++++
> >  lib/librte_eal/common/include/rte_devargs.h     | 18 ++++++++++++++++++
> >  lib/librte_eal/linuxapp/eal/rte_eal_version.map |  1 +
> >  4 files changed, 39 insertions(+)
> >
> > diff --git a/lib/librte_eal/bsdapp/eal/rte_eal_version.map b/lib/librte_eal/bsdapp/eal/rte_eal_version.map
> > index 381f895..40cd523 100644
> > --- a/lib/librte_eal/bsdapp/eal/rte_eal_version.map
> > +++ b/lib/librte_eal/bsdapp/eal/rte_eal_version.map
> > @@ -207,6 +207,7 @@ EXPERIMENTAL {
> >         global:
> >
> >         rte_eal_devargs_parse;
> > +       rte_eal_devargs_remove;
> >         rte_eal_hotplug_add;
> >         rte_eal_hotplug_remove;
> >
> > diff --git a/lib/librte_eal/common/eal_common_devargs.c b/lib/librte_eal/common/eal_common_devargs.c
> > index 49d43a3..bcdee13 100644
> > --- a/lib/librte_eal/common/eal_common_devargs.c
> > +++ b/lib/librte_eal/common/eal_common_devargs.c
> > @@ -41,6 +41,7 @@
> >  #include <string.h>
> >
> >  #include <rte_devargs.h>
> > +#include <rte_tailq.h>
> >  #include "eal_private.h"
> >
> >  /** Global list of user devices */
> > @@ -182,6 +183,24 @@ rte_eal_devargs_add(enum rte_devtype devtype, const char *devargs_str)
> >         return -1;
> >  }
> >
> > +int
> > +rte_eal_devargs_remove(const char *busname, const char *devname)
> > +{
> > +       struct rte_devargs *d;
> > +       void *tmp;
> > +
> > +       TAILQ_FOREACH_SAFE(d, &devargs_list, next, tmp) {
> > +               if (strcmp(d->bus->name, busname) == 0 &&
> > +                   strcmp(d->name, devname) == 0) {
> > +                       TAILQ_REMOVE(&devargs_list, d, next);
> > +                       free(d->args);
> > +                       free(d);
> > +                       return 0;
> > +               }
> > +       }
> > +       return 1;
> > +}
> > +
> >  /* count the number of devices of a specified type */
> >  unsigned int
> >  rte_eal_devargs_type_count(enum rte_devtype devtype)
> > diff --git a/lib/librte_eal/common/include/rte_devargs.h b/lib/librte_eal/common/include/rte_devargs.h
> > index a0427cd..36453b6 100644
> > --- a/lib/librte_eal/common/include/rte_devargs.h
> > +++ b/lib/librte_eal/common/include/rte_devargs.h
> > @@ -163,6 +163,24 @@ rte_eal_devargs_parse(const char *dev,
> >  int rte_eal_devargs_add(enum rte_devtype devtype, const char *devargs_str);
> >
> >  /**
> > + * Remove a device from the user device list.
> > + * Its resources are freed.
> > + * If the devargs cannot be found, nothing happens.
> > + *
> > + * @param busname
> > + *   bus name of the devargs to remove.
> > + *
> > + * @param devname
> > + *   device name of the devargs to remove.
> > + *
> > + * @return
> > + *   0 on success.
> > + *   <0 on error.
> > + *   >0 if the devargs was not within the user device list.
> > + */
> > +int rte_eal_devargs_remove(const char *busname, const char *devname);
> > +
> > +/**
> >   * Count the number of user devices of a specified type
> >   *
> >   * @param devtype
> > diff --git a/lib/librte_eal/linuxapp/eal/rte_eal_version.map b/lib/librte_eal/linuxapp/eal/rte_eal_version.map
> > index 0f9e009..a8ee349 100644
> > --- a/lib/librte_eal/linuxapp/eal/rte_eal_version.map
> > +++ b/lib/librte_eal/linuxapp/eal/rte_eal_version.map
> > @@ -212,6 +212,7 @@ EXPERIMENTAL {
> >         global:
> >
> >         rte_eal_devargs_parse;
> > +       rte_eal_devargs_remove;
> >         rte_eal_hotplug_add;
> >         rte_eal_hotplug_remove;
> >
> > --
> > 2.1.4
> >

-- 
Gaëtan Rivet
6WIND