[PATCH] qemu-options.hx: 9p: clarify -virtfs vs. -fsdev

[PATCH] qemu-options.hx: 9p: clarify -virtfs vs. -fsdev

[Christian Schoenebeck]

The docs are ambiguous about the difference (or actually their
equality) between options '-virtfs' vs. '-fsdev'. So clarify that
'-virtfs' is actually just a convenience shortcut for its
generalized form '-fsdev' in conjunction with '-device virtio-9p-pci'.

And as we're at it, also be a bit more descriptive what 9pfs is
actually used for.

Signed-off-by: Christian Schoenebeck <qemu_oss@crudebyte.com>
---
 qemu-options.hx | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/qemu-options.hx b/qemu-options.hx
index 962a5ebaa6..fd3830c6cd 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -1542,9 +1542,17 @@ SRST
 ``-virtfs proxy,sock_fd=sock_fd,mount_tag=mount_tag [,writeout=writeout][,readonly]``
   \
 ``-virtfs synth,mount_tag=mount_tag``
-    Define a new filesystem device and expose it to the guest using a
-    virtio-9p-device. The general form of a Virtual File system
-    pass-through options are:
+    Define a new virtual filesystem device and expose it to the guest using
+    a virtio-9p-device (a.k.a. 9pfs), which essentially means that a certain
+    directory on host is made directly accessible by guest as a pass-through
+    file system by using the 9P network protocol for communication between
+    host and guests, if desired even accessible, shared by several guests
+    simultaniously.
+
+    Note that ``-virtfs`` is actually just a convenience shortcut for its
+    generalized form ``-fsdev -device virtio-9p-pci``.
+
+    The general form of pass-through file system options are:
 
     ``local``
         Accesses to the filesystem are done by QEMU.
-- 
2.20.1

Re: [PATCH] qemu-options.hx: 9p: clarify -virtfs vs. -fsdev

[Cornelia Huck]

On Tue, 31 Mar 2020 15:23:38 +0200
Christian Schoenebeck <qemu_oss@crudebyte.com> wrote:

> The docs are ambiguous about the difference (or actually their
> equality) between options '-virtfs' vs. '-fsdev'. So clarify that
> '-virtfs' is actually just a convenience shortcut for its
> generalized form '-fsdev' in conjunction with '-device virtio-9p-pci'.
> 
> And as we're at it, also be a bit more descriptive what 9pfs is
> actually used for.
> 
> Signed-off-by: Christian Schoenebeck <qemu_oss@crudebyte.com>
> ---
>  qemu-options.hx | 14 +++++++++++---
>  1 file changed, 11 insertions(+), 3 deletions(-)
> 
> diff --git a/qemu-options.hx b/qemu-options.hx
> index 962a5ebaa6..fd3830c6cd 100644
> --- a/qemu-options.hx
> +++ b/qemu-options.hx
> @@ -1542,9 +1542,17 @@ SRST
>  ``-virtfs proxy,sock_fd=sock_fd,mount_tag=mount_tag [,writeout=writeout][,readonly]``
>    \
>  ``-virtfs synth,mount_tag=mount_tag``
> -    Define a new filesystem device and expose it to the guest using a
> -    virtio-9p-device. The general form of a Virtual File system
> -    pass-through options are:
> +    Define a new virtual filesystem device and expose it to the guest using
> +    a virtio-9p-device (a.k.a. 9pfs), which essentially means that a certain
> +    directory on host is made directly accessible by guest as a pass-through
> +    file system by using the 9P network protocol for communication between
> +    host and guests, if desired even accessible, shared by several guests
> +    simultaniously.
> +
> +    Note that ``-virtfs`` is actually just a convenience shortcut for its
> +    generalized form ``-fsdev -device virtio-9p-pci``.

Huh. This prompted me to try this on s390, and it actually creates a
virtio-9p-pci device there as well, not a virtio-9p-ccw device. A bit
surprising; but I don't see 9p used much (if at all) on s390 anyway.

> +
> +    The general form of pass-through file system options are:
>  
>      ``local``
>          Accesses to the filesystem are done by QEMU.

Good to see this spelled out:

Acked-by: Cornelia Huck <cohuck@redhat.com>

Re: [PATCH] qemu-options.hx: 9p: clarify -virtfs vs. -fsdev

[Christian Schoenebeck]

On Dienstag, 31. März 2020 17:27:27 CEST Cornelia Huck wrote:
> > diff --git a/qemu-options.hx b/qemu-options.hx
> > index 962a5ebaa6..fd3830c6cd 100644
> > --- a/qemu-options.hx
> > +++ b/qemu-options.hx
> > @@ -1542,9 +1542,17 @@ SRST
> > 
> >  ``-virtfs proxy,sock_fd=sock_fd,mount_tag=mount_tag
> >  [,writeout=writeout][,readonly]``>  
> >    \
> >  
> >  ``-virtfs synth,mount_tag=mount_tag``
> > 
> > -    Define a new filesystem device and expose it to the guest using a
> > -    virtio-9p-device. The general form of a Virtual File system
> > -    pass-through options are:
> > +    Define a new virtual filesystem device and expose it to the guest
> > using +    a virtio-9p-device (a.k.a. 9pfs), which essentially means that
> > a certain +    directory on host is made directly accessible by guest as
> > a pass-through +    file system by using the 9P network protocol for
> > communication between +    host and guests, if desired even accessible,
> > shared by several guests +    simultaniously.
> > +
> > +    Note that ``-virtfs`` is actually just a convenience shortcut for its
> > +    generalized form ``-fsdev -device virtio-9p-pci``.
> 
> Huh. This prompted me to try this on s390, and it actually creates a
> virtio-9p-pci device there as well, not a virtio-9p-ccw device. A bit
> surprising; but I don't see 9p used much (if at all) on s390 anyway.

Yeah, "virtio-9p-pci" is currently hard coded in softmmu/vl.c [line 3352]:
https://github.com/qemu/qemu/blob/17083d6d1e0635371418c26b613a6fa68d392f49/softmmu/vl.c#L3352

> > +
> > 
> > +    The general form of pass-through file system options are:
> >      ``local``
> >      
> >          Accesses to the filesystem are done by QEMU.
> 
> Good to see this spelled out:
> 
> Acked-by: Cornelia Huck <cohuck@redhat.com>

Best regards,
Christian Schoenebeck

Re: [PATCH] qemu-options.hx: 9p: clarify -virtfs vs. -fsdev

[Markus Armbruster]

Christian Schoenebeck <qemu_oss@crudebyte.com> writes:

> On Dienstag, 31. März 2020 17:27:27 CEST Cornelia Huck wrote:
>> > diff --git a/qemu-options.hx b/qemu-options.hx
>> > index 962a5ebaa6..fd3830c6cd 100644
>> > --- a/qemu-options.hx
>> > +++ b/qemu-options.hx
>> > @@ -1542,9 +1542,17 @@ SRST
>> > 
>> >  ``-virtfs proxy,sock_fd=sock_fd,mount_tag=mount_tag
>> >  [,writeout=writeout][,readonly]``>  
>> >    \
>> >  
>> >  ``-virtfs synth,mount_tag=mount_tag``
>> > 
>> > -    Define a new filesystem device and expose it to the guest using a
>> > -    virtio-9p-device. The general form of a Virtual File system
>> > -    pass-through options are:
>> > +    Define a new virtual filesystem device and expose it to the guest
>> > using +    a virtio-9p-device (a.k.a. 9pfs), which essentially means that
>> > a certain +    directory on host is made directly accessible by guest as
>> > a pass-through +    file system by using the 9P network protocol for
>> > communication between +    host and guests, if desired even accessible,
>> > shared by several guests +    simultaniously.
>> > +
>> > +    Note that ``-virtfs`` is actually just a convenience shortcut for its
>> > +    generalized form ``-fsdev -device virtio-9p-pci``.
>> 
>> Huh. This prompted me to try this on s390, and it actually creates a
>> virtio-9p-pci device there as well, not a virtio-9p-ccw device. A bit
>> surprising; but I don't see 9p used much (if at all) on s390 anyway.
>
> Yeah, "virtio-9p-pci" is currently hard coded in softmmu/vl.c [line 3352]:
> https://github.com/qemu/qemu/blob/17083d6d1e0635371418c26b613a6fa68d392f49/softmmu/vl.c#L3352

Should it be "virtio-9p" instead?  It's an alias for "virtio-9p-pci",
except for s390x, where it's an alias for "virtio-9p-ccw".

Re: [PATCH] qemu-options.hx: 9p: clarify -virtfs vs. -fsdev

[Cornelia Huck]

On Tue, 31 Mar 2020 18:05:08 +0200
Markus Armbruster <armbru@redhat.com> wrote:

> Christian Schoenebeck <qemu_oss@crudebyte.com> writes:
> 
> > On Dienstag, 31. März 2020 17:27:27 CEST Cornelia Huck wrote:  
> >> > diff --git a/qemu-options.hx b/qemu-options.hx
> >> > index 962a5ebaa6..fd3830c6cd 100644
> >> > --- a/qemu-options.hx
> >> > +++ b/qemu-options.hx
> >> > @@ -1542,9 +1542,17 @@ SRST
> >> > 
> >> >  ``-virtfs proxy,sock_fd=sock_fd,mount_tag=mount_tag  
> >> >  [,writeout=writeout][,readonly]``>    
> >> >    \
> >> >  
> >> >  ``-virtfs synth,mount_tag=mount_tag``
> >> > 
> >> > -    Define a new filesystem device and expose it to the guest using a
> >> > -    virtio-9p-device. The general form of a Virtual File system
> >> > -    pass-through options are:
> >> > +    Define a new virtual filesystem device and expose it to the guest
> >> > using +    a virtio-9p-device (a.k.a. 9pfs), which essentially means that
> >> > a certain +    directory on host is made directly accessible by guest as
> >> > a pass-through +    file system by using the 9P network protocol for
> >> > communication between +    host and guests, if desired even accessible,
> >> > shared by several guests +    simultaniously.
> >> > +
> >> > +    Note that ``-virtfs`` is actually just a convenience shortcut for its
> >> > +    generalized form ``-fsdev -device virtio-9p-pci``.  
> >> 
> >> Huh. This prompted me to try this on s390, and it actually creates a
> >> virtio-9p-pci device there as well, not a virtio-9p-ccw device. A bit
> >> surprising; but I don't see 9p used much (if at all) on s390 anyway.  
> >
> > Yeah, "virtio-9p-pci" is currently hard coded in softmmu/vl.c [line 3352]:
> > https://github.com/qemu/qemu/blob/17083d6d1e0635371418c26b613a6fa68d392f49/softmmu/vl.c#L3352  
> 
> Should it be "virtio-9p" instead?  It's an alias for "virtio-9p-pci",
> except for s390x, where it's an alias for "virtio-9p-ccw".

Seems like a reasonable change (although I'm not sure it matters too
much).

Re: [PATCH] qemu-options.hx: 9p: clarify -virtfs vs. -fsdev

[Christian Schoenebeck]

On Dienstag, 31. März 2020 18:10:33 CEST Cornelia Huck wrote:
> > >> Huh. This prompted me to try this on s390, and it actually creates a
> > >> virtio-9p-pci device there as well, not a virtio-9p-ccw device. A bit
> > >> surprising; but I don't see 9p used much (if at all) on s390 anyway.
> > > 
> > > Yeah, "virtio-9p-pci" is currently hard coded in softmmu/vl.c [line
> > > 3352]:
> > > https://github.com/qemu/qemu/blob/17083d6d1e0635371418c26b613a6fa68d392f
> > > 49/softmmu/vl.c#L3352> 
> > Should it be "virtio-9p" instead?  It's an alias for "virtio-9p-pci",
> > except for s390x, where it's an alias for "virtio-9p-ccw".
> 
> Seems like a reasonable change (although I'm not sure it matters too
> much).

It would be a minor change it seems, and yes there seems to be a virtio-9p-ccw 
implementation, however as long as nobody complains I leave it untouched for 
now. Especially since I have no idea about the s390 architecture, nor testing 
it.

Best regards,
Christian Schoenebeck

Re: [PATCH] qemu-options.hx: 9p: clarify -virtfs vs. -fsdev

[Greg Kurz]

On Tue, 31 Mar 2020 15:23:38 +0200
Christian Schoenebeck <qemu_oss@crudebyte.com> wrote:

> The docs are ambiguous about the difference (or actually their
> equality) between options '-virtfs' vs. '-fsdev'. So clarify that
> '-virtfs' is actually just a convenience shortcut for its
> generalized form '-fsdev' in conjunction with '-device virtio-9p-pci'.
> 
> And as we're at it, also be a bit more descriptive what 9pfs is
> actually used for.
> 
> Signed-off-by: Christian Schoenebeck <qemu_oss@crudebyte.com>
> ---

Applied to 9p-next.

>  qemu-options.hx | 14 +++++++++++---
>  1 file changed, 11 insertions(+), 3 deletions(-)
> 
> diff --git a/qemu-options.hx b/qemu-options.hx
> index 962a5ebaa6..fd3830c6cd 100644
> --- a/qemu-options.hx
> +++ b/qemu-options.hx
> @@ -1542,9 +1542,17 @@ SRST
>  ``-virtfs proxy,sock_fd=sock_fd,mount_tag=mount_tag [,writeout=writeout][,readonly]``
>    \
>  ``-virtfs synth,mount_tag=mount_tag``
> -    Define a new filesystem device and expose it to the guest using a
> -    virtio-9p-device. The general form of a Virtual File system
> -    pass-through options are:
> +    Define a new virtual filesystem device and expose it to the guest using
> +    a virtio-9p-device (a.k.a. 9pfs), which essentially means that a certain
> +    directory on host is made directly accessible by guest as a pass-through
> +    file system by using the 9P network protocol for communication between
> +    host and guests, if desired even accessible, shared by several guests
> +    simultaniously.
> +
> +    Note that ``-virtfs`` is actually just a convenience shortcut for its
> +    generalized form ``-fsdev -device virtio-9p-pci``.
> +
> +    The general form of pass-through file system options are:
>  
>      ``local``
>          Accesses to the filesystem are done by QEMU.