Re: [Xen-devel] [PATCH v6 04/12] xen: add basic hypervisor filesystem support

[Jürgen Groß <jgross@xxxxxxxx>]

On 03.03.20 17:59, Jan Beulich wrote:
> On 26.02.2020 13:46, Juergen Gross wrote:
> > --- /dev/null
> > +++ b/xen/common/hypfs.c
> > @@ -0,0 +1,349 @@
> > +/******************************************************************************
> > + *
> > + * hypfs.c
> > + *
> > + * Simple sysfs-like file system for the hypervisor.
> > + */
> > +
> > +#include <xen/err.h>
> > +#include <xen/guest_access.h>
> > +#include <xen/hypercall.h>
> > +#include <xen/hypfs.h>
> > +#include <xen/lib.h>
> > +#include <xen/rwlock.h>
> > +#include <public/hypfs.h>
> > +
> > +#ifdef CONFIG_COMPAT
> > +#include <compat/hypfs.h>
> > +CHECK_hypfs_direntry;
> > +#undef CHECK_hypfs_direntry
> > +#define CHECK_hypfs_direntry struct xen_hypfs_direntry
> I'm struggling to see why you need this #undef and #define.
Without those I get:

In file included from /home/gross/xen/unstable/xen/include/compat/xen.h:3:0,
                 from /home/gross/xen/unstable/xen/include/xen/shared.h:6,
                 from /home/gross/xen/unstable/xen/include/xen/sched.h:8,
                 from /home/gross/xen/unstable/xen/include/asm/paging.h:29,
                 from 
/home/gross/xen/unstable/xen/include/asm/guest_access.h:1,
                 from 
/home/gross/xen/unstable/xen/include/xen/guest_access.h:1,
                 from hypfs.c:9:
/home/gross/xen/unstable/xen/include/xen/compat.h:134:32: error: 
redefinition of ‘__checkFstruct_hypfs_direntry__flags’
 #define CHECK_NAME_(k, n, tag) __check ## tag ## k ## _ ## n
                                ^
/home/gross/xen/unstable/xen/include/xen/compat.h:166:34: note: in 
definition of macro ‘CHECK_FIELD_COMMON_’
 static inline int __maybe_unused name(k xen_ ## n *x, k compat_ ## n *c) \
                                  ^~~~
/home/gross/xen/unstable/xen/include/xen/compat.h:176:28: note: in 
expansion of macro ‘CHECK_NAME_’
     CHECK_FIELD_COMMON_(k, CHECK_NAME_(k, n ## __ ## f, F), n, f)
                            ^~~~~~~~~~~
/home/gross/xen/unstable/xen/include/compat/xlat.h:775:5: note: in 
expansion of macro ‘CHECK_FIELD_’
     CHECK_FIELD_(struct, hypfs_direntry, flags); \
     ^~~~~~~~~~~~
/home/gross/xen/unstable/xen/include/compat/xlat.h:782:5: note: in 
expansion of macro ‘CHECK_hypfs_direntry’
     CHECK_hypfs_direntry; \
     ^~~~~~~~~~~~~~~~~~~~
hypfs.c:19:1: note: in expansion of macro ‘CHECK_hypfs_dirlistentry’
 CHECK_hypfs_dirlistentry;
 ^~~~~~~~~~~~~~~~~~~~~~~~
/home/gross/xen/unstable/xen/include/xen/compat.h:134:32: note: previous 
definition of ‘__checkFstruct_hypfs_direntry__flags’ was here
 #define CHECK_NAME_(k, n, tag) __check ## tag ## k ## _ ## n
                                ^
/home/gross/xen/unstable/xen/include/xen/compat.h:166:34: note: in 
definition of macro ‘CHECK_FIELD_COMMON_’
 static inline int __maybe_unused name(k xen_ ## n *x, k compat_ ## n *c) \
                                  ^~~~
/home/gross/xen/unstable/xen/include/xen/compat.h:176:28: note: in 
expansion of macro ‘CHECK_NAME_’
     CHECK_FIELD_COMMON_(k, CHECK_NAME_(k, n ## __ ## f, F), n, f)
                            ^~~~~~~~~~~
/home/gross/xen/unstable/xen/include/compat/xlat.h:775:5: note: in 
expansion of macro ‘CHECK_FIELD_’
     CHECK_FIELD_(struct, hypfs_direntry, flags); \
     ^~~~~~~~~~~~
hypfs.c:18:1: note: in expansion of macro ‘CHECK_hypfs_direntry’
 CHECK_hypfs_direntry;


> > +int hypfs_write_leaf(struct hypfs_entry_leaf *leaf,
> > +                     XEN_GUEST_HANDLE_PARAM(void) uaddr, unsigned long ulen)
> > +{
> > +    char *buf;
> > +    int ret;
> > +
> > +    if ( ulen > leaf->e.size )
> > +        return -ENOSPC;
> > +
> > +    if ( leaf->e.type != XEN_HYPFS_TYPE_STRING &&
> > +         leaf->e.type != XEN_HYPFS_TYPE_BLOB && ulen != leaf->e.size )
> > +        return -EDOM;
> Why the exception of string and blob? My concern about the
> meaning of a partially written entry (without its size having
> changed) remains.
It is perfectly valid to write a shorter string into a character
array. I could drop the blob here, but in the end I think allowing
for a blob to change the size should be fine.

> > +    buf = xmalloc_array(char, ulen);
> > +    if ( !buf )
> > +        return -ENOMEM;
> > +
> > +    ret = -EFAULT;
> > +    if ( copy_from_guest(buf, uaddr, ulen) )
> > +        goto out;
> > +
> > +    ret = -EINVAL;
> > +    if ( leaf->e.type == XEN_HYPFS_TYPE_STRING && !memchr(buf, 0, ulen) )
> This should also use the != buf + ulen - 1 form imo.
I'm fine to change that, but should the hypervisor really refuse to
accept a larger buffer?


Juergen

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxxx
https://lists.xenproject.org/mailman/listinfo/xen-devel