[PATCH [repost]] block/blkio: Don't assume size_t is 64 bit

[PATCH [repost]] block/blkio: Don't assume size_t is 64 bit

[Richard W.M. Jones]

Repost of the same patch as a minute ago because I messed up a couple
of email addresses in the CC.

Rich.

[PATCH [repost]] block/blkio: Don't assume size_t is 64 bit

[Richard W.M. Jones]

With GCC 14 the code failed to compile on i686 (and was wrong for any
version of GCC):

../block/blkio.c: In function ‘blkio_file_open’:
../block/blkio.c:857:28: error: passing argument 3 of ‘blkio_get_uint64’ from incompatible pointer type [-Wincompatible-pointer-types]
  857 |                            &s->mem_region_alignment);
      |                            ^~~~~~~~~~~~~~~~~~~~~~~~
      |                            |
      |                            size_t * {aka unsigned int *}
In file included from ../block/blkio.c:12:
/usr/include/blkio.h:49:67: note: expected ‘uint64_t *’ {aka ‘long long unsigned int *’} but argument is of type ‘size_t *’ {aka ‘unsigned int *’}
   49 | int blkio_get_uint64(struct blkio *b, const char *name, uint64_t *value);
      |                                                         ~~~~~~~~~~^~~~~

Signed-off-by: Richard W.M. Jones <rjones@redhat.com>
---
 block/blkio.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/block/blkio.c b/block/blkio.c
index 0a0a6c0f5fd..52d78935147 100644
--- a/block/blkio.c
+++ b/block/blkio.c
@@ -794,6 +794,7 @@ static int blkio_file_open(BlockDriverState *bs, QDict *options, int flags,
     const char *blkio_driver = bs->drv->protocol_name;
     BDRVBlkioState *s = bs->opaque;
     int ret;
+    uint64_t val;
 
     ret = blkio_create(blkio_driver, &s->blkio);
     if (ret < 0) {
@@ -854,7 +855,7 @@ static int blkio_file_open(BlockDriverState *bs, QDict *options, int flags,
 
     ret = blkio_get_uint64(s->blkio,
                            "mem-region-alignment",
-                           &s->mem_region_alignment);
+                           &val);
     if (ret < 0) {
         error_setg_errno(errp, -ret,
                          "failed to get mem-region-alignment: %s",
@@ -862,6 +863,15 @@ static int blkio_file_open(BlockDriverState *bs, QDict *options, int flags,
         blkio_destroy(&s->blkio);
         return ret;
     }
+#if HOST_LONG_BITS == 32
+    if (val > SIZE_MAX) {
+        error_setg_errno(errp, ERANGE,
+                         "mem-region-alignment too large for size_t");
+        blkio_destroy(&s->blkio);
+        return -ERANGE;
+    }
+#endif
+    s->mem_region_alignment = (size_t)val;
 
     ret = blkio_get_bool(s->blkio,
                          "may-pin-mem-regions",
-- 
2.43.0

Re: [PATCH [repost]] block/blkio: Don't assume size_t is 64 bit

[Eric Blake]

On Mon, Jan 29, 2024 at 06:53:55PM +0000, Richard W.M. Jones wrote:
> With GCC 14 the code failed to compile on i686 (and was wrong for any
> version of GCC):
> 
> ../block/blkio.c: In function ‘blkio_file_open’:
> ../block/blkio.c:857:28: error: passing argument 3 of ‘blkio_get_uint64’ from incompatible pointer type [-Wincompatible-pointer-types]
>   857 |                            &s->mem_region_alignment);
>       |                            ^~~~~~~~~~~~~~~~~~~~~~~~
>       |                            |
>       |                            size_t * {aka unsigned int *}
> In file included from ../block/blkio.c:12:
> /usr/include/blkio.h:49:67: note: expected ‘uint64_t *’ {aka ‘long long unsigned int *’} but argument is of type ‘size_t *’ {aka ‘unsigned int *’}
>    49 | int blkio_get_uint64(struct blkio *b, const char *name, uint64_t *value);
>       |                                                         ~~~~~~~~~~^~~~~

I wish gcc could point this out even when compiling on a 64-bit
platform where size_t and uint64_t happen to share the same type, by
reasoning about the underlying typedefs being different.  But that's a
bigger task for gcc, and not one for this group.

> 
> Signed-off-by: Richard W.M. Jones <rjones@redhat.com>
> ---
>  block/blkio.c | 12 +++++++++++-
>  1 file changed, 11 insertions(+), 1 deletion(-)

Reviewed-by: Eric Blake <eblake@redhat.com>

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.
Virtualization:  qemu.org | libguestfs.org

Re: [PATCH [repost]] block/blkio: Don't assume size_t is 64 bit

[Kevin Wolf]

Am 29.01.2024 um 19:53 hat Richard W.M. Jones geschrieben:
> With GCC 14 the code failed to compile on i686 (and was wrong for any
> version of GCC):
> 
> ../block/blkio.c: In function ‘blkio_file_open’:
> ../block/blkio.c:857:28: error: passing argument 3 of ‘blkio_get_uint64’ from incompatible pointer type [-Wincompatible-pointer-types]
>   857 |                            &s->mem_region_alignment);
>       |                            ^~~~~~~~~~~~~~~~~~~~~~~~
>       |                            |
>       |                            size_t * {aka unsigned int *}
> In file included from ../block/blkio.c:12:
> /usr/include/blkio.h:49:67: note: expected ‘uint64_t *’ {aka ‘long long unsigned int *’} but argument is of type ‘size_t *’ {aka ‘unsigned int *’}
>    49 | int blkio_get_uint64(struct blkio *b, const char *name, uint64_t *value);
>       |                                                         ~~~~~~~~~~^~~~~
> 
> Signed-off-by: Richard W.M. Jones <rjones@redhat.com>

Why not simply make BDRVBlkioState.mem_region_alignment a uint64_t
instead of keeping it size_t and doing an additional conversion with
a check that requires an #if (probably to avoid a warning on 64 bit
hosts because the condition is never true)?

Kevin

>  block/blkio.c | 12 +++++++++++-
>  1 file changed, 11 insertions(+), 1 deletion(-)
> 
> diff --git a/block/blkio.c b/block/blkio.c
> index 0a0a6c0f5fd..52d78935147 100644
> --- a/block/blkio.c
> +++ b/block/blkio.c
> @@ -794,6 +794,7 @@ static int blkio_file_open(BlockDriverState *bs, QDict *options, int flags,
>      const char *blkio_driver = bs->drv->protocol_name;
>      BDRVBlkioState *s = bs->opaque;
>      int ret;
> +    uint64_t val;
>  
>      ret = blkio_create(blkio_driver, &s->blkio);
>      if (ret < 0) {
> @@ -854,7 +855,7 @@ static int blkio_file_open(BlockDriverState *bs, QDict *options, int flags,
>  
>      ret = blkio_get_uint64(s->blkio,
>                             "mem-region-alignment",
> -                           &s->mem_region_alignment);
> +                           &val);
>      if (ret < 0) {
>          error_setg_errno(errp, -ret,
>                           "failed to get mem-region-alignment: %s",
> @@ -862,6 +863,15 @@ static int blkio_file_open(BlockDriverState *bs, QDict *options, int flags,
>          blkio_destroy(&s->blkio);
>          return ret;
>      }
> +#if HOST_LONG_BITS == 32
> +    if (val > SIZE_MAX) {
> +        error_setg_errno(errp, ERANGE,
> +                         "mem-region-alignment too large for size_t");
> +        blkio_destroy(&s->blkio);
> +        return -ERANGE;
> +    }
> +#endif
> +    s->mem_region_alignment = (size_t)val;
>  
>      ret = blkio_get_bool(s->blkio,
>                           "may-pin-mem-regions",
> -- 
> 2.43.0
> 

Re: [PATCH [repost]] block/blkio: Don't assume size_t is 64 bit

[Richard W.M. Jones]

[-- Attachment #1: Type: text/plain, Size: 3571 bytes --]

On Tue, Jan 30, 2024 at 09:51:59AM +0100, Kevin Wolf wrote:
> Am 29.01.2024 um 19:53 hat Richard W.M. Jones geschrieben:
> > With GCC 14 the code failed to compile on i686 (and was wrong for any
> > version of GCC):
> > 
> > ../block/blkio.c: In function ‘blkio_file_open’:
> > ../block/blkio.c:857:28: error: passing argument 3 of ‘blkio_get_uint64’ from incompatible pointer type [-Wincompatible-pointer-types]
> >   857 |                            &s->mem_region_alignment);
> >       |                            ^~~~~~~~~~~~~~~~~~~~~~~~
> >       |                            |
> >       |                            size_t * {aka unsigned int *}
> > In file included from ../block/blkio.c:12:
> > /usr/include/blkio.h:49:67: note: expected ‘uint64_t *’ {aka ‘long long unsigned int *’} but argument is of type ‘size_t *’ {aka ‘unsigned int *’}
> >    49 | int blkio_get_uint64(struct blkio *b, const char *name, uint64_t *value);
> >       |                                                         ~~~~~~~~~~^~~~~
> > 
> > Signed-off-by: Richard W.M. Jones <rjones@redhat.com>
> 
> Why not simply make BDRVBlkioState.mem_region_alignment a uint64_t
> instead of keeping it size_t and doing an additional conversion with
> a check that requires an #if (probably to avoid a warning on 64 bit
> hosts because the condition is never true)?

The smaller change (attached) does work on i686, but this worries me a
little (although it doesn't give any error or warning):

    if (((uintptr_t)host | size) % s->mem_region_alignment) {
    error_setg(errp, "unaligned buf %p with size %zu", host, size);
        return BMRR_FAIL;
    }

Rich.

> Kevin
> 
> >  block/blkio.c | 12 +++++++++++-
> >  1 file changed, 11 insertions(+), 1 deletion(-)
> > 
> > diff --git a/block/blkio.c b/block/blkio.c
> > index 0a0a6c0f5fd..52d78935147 100644
> > --- a/block/blkio.c
> > +++ b/block/blkio.c
> > @@ -794,6 +794,7 @@ static int blkio_file_open(BlockDriverState *bs, QDict *options, int flags,
> >      const char *blkio_driver = bs->drv->protocol_name;
> >      BDRVBlkioState *s = bs->opaque;
> >      int ret;
> > +    uint64_t val;
> >  
> >      ret = blkio_create(blkio_driver, &s->blkio);
> >      if (ret < 0) {
> > @@ -854,7 +855,7 @@ static int blkio_file_open(BlockDriverState *bs, QDict *options, int flags,
> >  
> >      ret = blkio_get_uint64(s->blkio,
> >                             "mem-region-alignment",
> > -                           &s->mem_region_alignment);
> > +                           &val);
> >      if (ret < 0) {
> >          error_setg_errno(errp, -ret,
> >                           "failed to get mem-region-alignment: %s",
> > @@ -862,6 +863,15 @@ static int blkio_file_open(BlockDriverState *bs, QDict *options, int flags,
> >          blkio_destroy(&s->blkio);
> >          return ret;
> >      }
> > +#if HOST_LONG_BITS == 32
> > +    if (val > SIZE_MAX) {
> > +        error_setg_errno(errp, ERANGE,
> > +                         "mem-region-alignment too large for size_t");
> > +        blkio_destroy(&s->blkio);
> > +        return -ERANGE;
> > +    }
> > +#endif
> > +    s->mem_region_alignment = (size_t)val;
> >  
> >      ret = blkio_get_bool(s->blkio,
> >                           "may-pin-mem-regions",
> > -- 
> > 2.43.0
> > 

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
libguestfs lets you edit virtual machines.  Supports shell scripting,
bindings from many languages.  http://libguestfs.org

[-- Attachment #2: 0001-block-blkio-Make-s-mem_region_alignment-be-64-bits.patch --]
[-- Type: text/plain, Size: 1738 bytes --]

From 500f3a81652dcefa79a4864c1f3fa6747c16952e Mon Sep 17 00:00:00 2001
From: "Richard W.M. Jones" <rjones@redhat.com>
Date: Mon, 29 Jan 2024 18:20:46 +0000
Subject: [PATCH] block/blkio: Make s->mem_region_alignment be 64 bits
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

With GCC 14 the code failed to compile on i686 (and was wrong for any
version of GCC):

../block/blkio.c: In function ‘blkio_file_open’:
../block/blkio.c:857:28: error: passing argument 3 of ‘blkio_get_uint64’ from incompatible pointer type [-Wincompatible-pointer-types]
  857 |                            &s->mem_region_alignment);
      |                            ^~~~~~~~~~~~~~~~~~~~~~~~
      |                            |
      |                            size_t * {aka unsigned int *}
In file included from ../block/blkio.c:12:
/usr/include/blkio.h:49:67: note: expected ‘uint64_t *’ {aka ‘long long unsigned int *’} but argument is of type ‘size_t *’ {aka ‘unsigned int *’}
   49 | int blkio_get_uint64(struct blkio *b, const char *name, uint64_t *value);
      |                                                         ~~~~~~~~~~^~~~~

Signed-off-by: Richard W.M. Jones <rjones@redhat.com>
---
 block/blkio.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/block/blkio.c b/block/blkio.c
index 0a0a6c0f5fd..bc2f21784c7 100644
--- a/block/blkio.c
+++ b/block/blkio.c
@@ -68,7 +68,7 @@ typedef struct {
     CoQueue bounce_available;
 
     /* The value of the "mem-region-alignment" property */
-    size_t mem_region_alignment;
+    uint64_t mem_region_alignment;
 
     /* Can we skip adding/deleting blkio_mem_regions? */
     bool needs_mem_regions;
-- 
2.43.0

Re: [PATCH [repost]] block/blkio: Don't assume size_t is 64 bit

[Kevin Wolf]

Am 30.01.2024 um 11:30 hat Richard W.M. Jones geschrieben:
> On Tue, Jan 30, 2024 at 09:51:59AM +0100, Kevin Wolf wrote:
> > Am 29.01.2024 um 19:53 hat Richard W.M. Jones geschrieben:
> > > With GCC 14 the code failed to compile on i686 (and was wrong for any
> > > version of GCC):
> > > 
> > > ../block/blkio.c: In function ‘blkio_file_open’:
> > > ../block/blkio.c:857:28: error: passing argument 3 of ‘blkio_get_uint64’ from incompatible pointer type [-Wincompatible-pointer-types]
> > >   857 |                            &s->mem_region_alignment);
> > >       |                            ^~~~~~~~~~~~~~~~~~~~~~~~
> > >       |                            |
> > >       |                            size_t * {aka unsigned int *}
> > > In file included from ../block/blkio.c:12:
> > > /usr/include/blkio.h:49:67: note: expected ‘uint64_t *’ {aka ‘long long unsigned int *’} but argument is of type ‘size_t *’ {aka ‘unsigned int *’}
> > >    49 | int blkio_get_uint64(struct blkio *b, const char *name, uint64_t *value);
> > >       |                                                         ~~~~~~~~~~^~~~~
> > > 
> > > Signed-off-by: Richard W.M. Jones <rjones@redhat.com>
> > 
> > Why not simply make BDRVBlkioState.mem_region_alignment a uint64_t
> > instead of keeping it size_t and doing an additional conversion with
> > a check that requires an #if (probably to avoid a warning on 64 bit
> > hosts because the condition is never true)?
> 
> The smaller change (attached) does work on i686, but this worries me a
> little (although it doesn't give any error or warning):
> 
>     if (((uintptr_t)host | size) % s->mem_region_alignment) {
>     error_setg(errp, "unaligned buf %p with size %zu", host, size);
>         return BMRR_FAIL;
>     }

I don't see the problem? The calculation will now be done in 64 bits
even on a 32 bit host, but that seems fine to me. Is there a trap I'm
missing?

Kevin

> From 500f3a81652dcefa79a4864c1f3fa6747c16952e Mon Sep 17 00:00:00 2001
> From: "Richard W.M. Jones" <rjones@redhat.com>
> Date: Mon, 29 Jan 2024 18:20:46 +0000
> Subject: [PATCH] block/blkio: Make s->mem_region_alignment be 64 bits
> MIME-Version: 1.0
> Content-Type: text/plain; charset=UTF-8
> Content-Transfer-Encoding: 8bit
> 
> With GCC 14 the code failed to compile on i686 (and was wrong for any
> version of GCC):
> 
> ../block/blkio.c: In function ‘blkio_file_open’:
> ../block/blkio.c:857:28: error: passing argument 3 of ‘blkio_get_uint64’ from incompatible pointer type [-Wincompatible-pointer-types]
>   857 |                            &s->mem_region_alignment);
>       |                            ^~~~~~~~~~~~~~~~~~~~~~~~
>       |                            |
>       |                            size_t * {aka unsigned int *}
> In file included from ../block/blkio.c:12:
> /usr/include/blkio.h:49:67: note: expected ‘uint64_t *’ {aka ‘long long unsigned int *’} but argument is of type ‘size_t *’ {aka ‘unsigned int *’}
>    49 | int blkio_get_uint64(struct blkio *b, const char *name, uint64_t *value);
>       |                                                         ~~~~~~~~~~^~~~~
> 
> Signed-off-by: Richard W.M. Jones <rjones@redhat.com>
> ---
>  block/blkio.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/block/blkio.c b/block/blkio.c
> index 0a0a6c0f5fd..bc2f21784c7 100644
> --- a/block/blkio.c
> +++ b/block/blkio.c
> @@ -68,7 +68,7 @@ typedef struct {
>      CoQueue bounce_available;
>  
>      /* The value of the "mem-region-alignment" property */
> -    size_t mem_region_alignment;
> +    uint64_t mem_region_alignment;
>  
>      /* Can we skip adding/deleting blkio_mem_regions? */
>      bool needs_mem_regions;
> -- 
> 2.43.0
> 

Re: [PATCH [repost]] block/blkio: Don't assume size_t is 64 bit

[Richard W.M. Jones]

On Tue, Jan 30, 2024 at 01:04:46PM +0100, Kevin Wolf wrote:
> Am 30.01.2024 um 11:30 hat Richard W.M. Jones geschrieben:
> > On Tue, Jan 30, 2024 at 09:51:59AM +0100, Kevin Wolf wrote:
> > > Am 29.01.2024 um 19:53 hat Richard W.M. Jones geschrieben:
> > > > With GCC 14 the code failed to compile on i686 (and was wrong for any
> > > > version of GCC):
> > > > 
> > > > ../block/blkio.c: In function ‘blkio_file_open’:
> > > > ../block/blkio.c:857:28: error: passing argument 3 of ‘blkio_get_uint64’ from incompatible pointer type [-Wincompatible-pointer-types]
> > > >   857 |                            &s->mem_region_alignment);
> > > >       |                            ^~~~~~~~~~~~~~~~~~~~~~~~
> > > >       |                            |
> > > >       |                            size_t * {aka unsigned int *}
> > > > In file included from ../block/blkio.c:12:
> > > > /usr/include/blkio.h:49:67: note: expected ‘uint64_t *’ {aka ‘long long unsigned int *’} but argument is of type ‘size_t *’ {aka ‘unsigned int *’}
> > > >    49 | int blkio_get_uint64(struct blkio *b, const char *name, uint64_t *value);
> > > >       |                                                         ~~~~~~~~~~^~~~~
> > > > 
> > > > Signed-off-by: Richard W.M. Jones <rjones@redhat.com>
> > > 
> > > Why not simply make BDRVBlkioState.mem_region_alignment a uint64_t
> > > instead of keeping it size_t and doing an additional conversion with
> > > a check that requires an #if (probably to avoid a warning on 64 bit
> > > hosts because the condition is never true)?
> > 
> > The smaller change (attached) does work on i686, but this worries me a
> > little (although it doesn't give any error or warning):
> > 
> >     if (((uintptr_t)host | size) % s->mem_region_alignment) {
> >     error_setg(errp, "unaligned buf %p with size %zu", host, size);
> >         return BMRR_FAIL;
> >     }
> 
> I don't see the problem? The calculation will now be done in 64 bits
> even on a 32 bit host, but that seems fine to me. Is there a trap I'm
> missing?

I guess not.  Stefan, any comments on whether we need to worry about
huge mem-region-alignment?  I'll post the updated patch as a new
message in a second.

Rich.

> Kevin
> 
> > From 500f3a81652dcefa79a4864c1f3fa6747c16952e Mon Sep 17 00:00:00 2001
> > From: "Richard W.M. Jones" <rjones@redhat.com>
> > Date: Mon, 29 Jan 2024 18:20:46 +0000
> > Subject: [PATCH] block/blkio: Make s->mem_region_alignment be 64 bits
> > MIME-Version: 1.0
> > Content-Type: text/plain; charset=UTF-8
> > Content-Transfer-Encoding: 8bit
> > 
> > With GCC 14 the code failed to compile on i686 (and was wrong for any
> > version of GCC):
> > 
> > ../block/blkio.c: In function ‘blkio_file_open’:
> > ../block/blkio.c:857:28: error: passing argument 3 of ‘blkio_get_uint64’ from incompatible pointer type [-Wincompatible-pointer-types]
> >   857 |                            &s->mem_region_alignment);
> >       |                            ^~~~~~~~~~~~~~~~~~~~~~~~
> >       |                            |
> >       |                            size_t * {aka unsigned int *}
> > In file included from ../block/blkio.c:12:
> > /usr/include/blkio.h:49:67: note: expected ‘uint64_t *’ {aka ‘long long unsigned int *’} but argument is of type ‘size_t *’ {aka ‘unsigned int *’}
> >    49 | int blkio_get_uint64(struct blkio *b, const char *name, uint64_t *value);
> >       |                                                         ~~~~~~~~~~^~~~~
> > 
> > Signed-off-by: Richard W.M. Jones <rjones@redhat.com>
> > ---
> >  block/blkio.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/block/blkio.c b/block/blkio.c
> > index 0a0a6c0f5fd..bc2f21784c7 100644
> > --- a/block/blkio.c
> > +++ b/block/blkio.c
> > @@ -68,7 +68,7 @@ typedef struct {
> >      CoQueue bounce_available;
> >  
> >      /* The value of the "mem-region-alignment" property */
> > -    size_t mem_region_alignment;
> > +    uint64_t mem_region_alignment;
> >  
> >      /* Can we skip adding/deleting blkio_mem_regions? */
> >      bool needs_mem_regions;
> > -- 
> > 2.43.0
> > 

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
Fedora Windows cross-compiler. Compile Windows programs, test, and
build Windows installers. Over 100 libraries supported.
http://fedoraproject.org/wiki/MinGW

Re: [PATCH [repost]] block/blkio: Don't assume size_t is 64 bit

[Stefan Hajnoczi]

[-- Attachment #1: Type: text/plain, Size: 2498 bytes --]

On Tue, Jan 30, 2024 at 12:19:37PM +0000, Richard W.M. Jones wrote:
> On Tue, Jan 30, 2024 at 01:04:46PM +0100, Kevin Wolf wrote:
> > Am 30.01.2024 um 11:30 hat Richard W.M. Jones geschrieben:
> > > On Tue, Jan 30, 2024 at 09:51:59AM +0100, Kevin Wolf wrote:
> > > > Am 29.01.2024 um 19:53 hat Richard W.M. Jones geschrieben:
> > > > > With GCC 14 the code failed to compile on i686 (and was wrong for any
> > > > > version of GCC):
> > > > > 
> > > > > ../block/blkio.c: In function ‘blkio_file_open’:
> > > > > ../block/blkio.c:857:28: error: passing argument 3 of ‘blkio_get_uint64’ from incompatible pointer type [-Wincompatible-pointer-types]
> > > > >   857 |                            &s->mem_region_alignment);
> > > > >       |                            ^~~~~~~~~~~~~~~~~~~~~~~~
> > > > >       |                            |
> > > > >       |                            size_t * {aka unsigned int *}
> > > > > In file included from ../block/blkio.c:12:
> > > > > /usr/include/blkio.h:49:67: note: expected ‘uint64_t *’ {aka ‘long long unsigned int *’} but argument is of type ‘size_t *’ {aka ‘unsigned int *’}
> > > > >    49 | int blkio_get_uint64(struct blkio *b, const char *name, uint64_t *value);
> > > > >       |                                                         ~~~~~~~~~~^~~~~
> > > > > 
> > > > > Signed-off-by: Richard W.M. Jones <rjones@redhat.com>
> > > > 
> > > > Why not simply make BDRVBlkioState.mem_region_alignment a uint64_t
> > > > instead of keeping it size_t and doing an additional conversion with
> > > > a check that requires an #if (probably to avoid a warning on 64 bit
> > > > hosts because the condition is never true)?
> > > 
> > > The smaller change (attached) does work on i686, but this worries me a
> > > little (although it doesn't give any error or warning):
> > > 
> > >     if (((uintptr_t)host | size) % s->mem_region_alignment) {
> > >     error_setg(errp, "unaligned buf %p with size %zu", host, size);
> > >         return BMRR_FAIL;
> > >     }
> > 
> > I don't see the problem? The calculation will now be done in 64 bits
> > even on a 32 bit host, but that seems fine to me. Is there a trap I'm
> > missing?
> 
> I guess not.  Stefan, any comments on whether we need to worry about
> huge mem-region-alignment?  I'll post the updated patch as a new
> message in a second.

An alignment of 32 or more bits is not required in any scenario that I'm
aware of.

Stefan

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