diff mbox

[for-2.3,v2,3/6] vmdk: Clean up descriptor file reading

Message ID 87fvcxqh2c.fsf@blackfin.pond.sub.org
State New
Headers show

Commit Message

Markus Armbruster Dec. 3, 2014, 8:21 a.m. UTC 
Fam Zheng <famz@redhat.com> writes:

> Zeroing a buffer that will be filled right after is not necessary, and
> allocating a power of two + 1 is naughty.
>
> Suggested-by: Markus Armbruster <armbru@redhat.com>
> Signed-off-by: Fam Zheng <famz@redhat.com>
> ---
>  block/vmdk.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/block/vmdk.c b/block/vmdk.c
> index 28d22db..e863a09 100644
> --- a/block/vmdk.c
> +++ b/block/vmdk.c
> @@ -558,14 +558,15 @@ static char *vmdk_read_desc(BlockDriverState *file, uint64_t desc_offset,
>      }
>  
       size = bdrv_getlength(file);
       if (size < 0) {
           error_setg_errno(errp, -size, "Could not access file");
           return NULL;
       }

>      size = MIN(size, 1 << 20);  /* avoid unbounded allocation */

Consider the case where size <= 1 << 20, i.e. this line is a no-op.

> -    buf = g_malloc0(size + 1);
> +    buf = g_malloc(size);
>  
> -    ret = bdrv_pread(file, desc_offset, buf, size);
> +    ret = bdrv_pread(file, desc_offset, buf, size - 1);

Then this reads everything except the last byte (thanks to Don for
spotting it).

>      if (ret < 0) {
>          error_setg_errno(errp, -ret, "Could not read from file");
>          g_free(buf);
>          return NULL;
>      }
> +    buf[ret] = 0;
>  
>      return buf;
>  }

I figure Don suggested this instead:

Comments

Fam Zheng Dec. 3, 2014, 9:20 a.m. UTC | #1 
On Wed, 12/03 09:21, Markus Armbruster wrote:
> Fam Zheng <famz@redhat.com> writes:
> 
> > Zeroing a buffer that will be filled right after is not necessary, and
> > allocating a power of two + 1 is naughty.
> >
> > Suggested-by: Markus Armbruster <armbru@redhat.com>
> > Signed-off-by: Fam Zheng <famz@redhat.com>
> > ---
> >  block/vmdk.c | 5 +++--
> >  1 file changed, 3 insertions(+), 2 deletions(-)
> >
> > diff --git a/block/vmdk.c b/block/vmdk.c
> > index 28d22db..e863a09 100644
> > --- a/block/vmdk.c
> > +++ b/block/vmdk.c
> > @@ -558,14 +558,15 @@ static char *vmdk_read_desc(BlockDriverState *file, uint64_t desc_offset,
> >      }
> >  
>        size = bdrv_getlength(file);
>        if (size < 0) {
>            error_setg_errno(errp, -size, "Could not access file");
>            return NULL;
>        }
> 
> >      size = MIN(size, 1 << 20);  /* avoid unbounded allocation */
> 
> Consider the case where size <= 1 << 20, i.e. this line is a no-op.
> 
> > -    buf = g_malloc0(size + 1);
> > +    buf = g_malloc(size);
> >  
> > -    ret = bdrv_pread(file, desc_offset, buf, size);
> > +    ret = bdrv_pread(file, desc_offset, buf, size - 1);
> 
> Then this reads everything except the last byte (thanks to Don for
> spotting it).

Yes, I was wrong.

> 
> >      if (ret < 0) {
> >          error_setg_errno(errp, -ret, "Could not read from file");
> >          g_free(buf);
> >          return NULL;
> >      }
> > +    buf[ret] = 0;
> >  
> >      return buf;
> >  }
> 
> I figure Don suggested this instead:

Yes. Thanks.

Fam

> 
> diff --git a/block/vmdk.c b/block/vmdk.c
> index 2cbfd3e..b7feb15 100644
> --- a/block/vmdk.c
> +++ b/block/vmdk.c
> @@ -556,8 +556,8 @@ static char *vmdk_read_desc(BlockDriverState *file, uint64_t desc_offset,
>          return NULL;
>      }
>  
> -    size = MIN(size, 1 << 20);  /* avoid unbounded allocation */
> -    buf = g_malloc0(size + 1);
> +    size = MIN(size, (1 << 20) - 1);  /* avoid unbounded allocation */
> +    buf = g_malloc(size + 1);
>  
>      ret = bdrv_pread(file, desc_offset, buf, size);
>      if (ret < 0) {
> @@ -565,6 +565,7 @@ static char *vmdk_read_desc(BlockDriverState *file, uint64_t desc_offset,
>          g_free(buf);
>          return NULL;
>      }
> +    buf[ret] = 0;
>  
>      return buf;
>  }
Don Koch Dec. 3, 2014, 4:43 p.m. UTC | #2 
On Wed, 3 Dec 2014 17:20:27 +0800
Fam Zheng <famz@redhat.com> wrote:

> On Wed, 12/03 09:21, Markus Armbruster wrote:
> > Fam Zheng <famz@redhat.com> writes:
> > 
> > > Zeroing a buffer that will be filled right after is not necessary, and
> > > allocating a power of two + 1 is naughty.
> > >
> > > Suggested-by: Markus Armbruster <armbru@redhat.com>
> > > Signed-off-by: Fam Zheng <famz@redhat.com>
> > > ---
> > >  block/vmdk.c | 5 +++--
> > >  1 file changed, 3 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/block/vmdk.c b/block/vmdk.c
> > > index 28d22db..e863a09 100644
> > > --- a/block/vmdk.c
> > > +++ b/block/vmdk.c
> > > @@ -558,14 +558,15 @@ static char *vmdk_read_desc(BlockDriverState *file, uint64_t desc_offset,
> > >      }
> > >  
> >        size = bdrv_getlength(file);
> >        if (size < 0) {
> >            error_setg_errno(errp, -size, "Could not access file");
> >            return NULL;
> >        }
> > 
> > >      size = MIN(size, 1 << 20);  /* avoid unbounded allocation */
> > 
> > Consider the case where size <= 1 << 20, i.e. this line is a no-op.
> > 
> > > -    buf = g_malloc0(size + 1);
> > > +    buf = g_malloc(size);
> > >  
> > > -    ret = bdrv_pread(file, desc_offset, buf, size);
> > > +    ret = bdrv_pread(file, desc_offset, buf, size - 1);
> > 
> > Then this reads everything except the last byte (thanks to Don for
> > spotting it).
> 
> Yes, I was wrong.
> 
> > 
> > >      if (ret < 0) {
> > >          error_setg_errno(errp, -ret, "Could not read from file");
> > >          g_free(buf);
> > >          return NULL;
> > >      }
> > > +    buf[ret] = 0;
> > >  
> > >      return buf;
> > >  }
> > 
> > I figure Don suggested this instead:

Correct.

> 
> Yes. Thanks.
> 
> Fam
> 
> > 
> > diff --git a/block/vmdk.c b/block/vmdk.c
> > index 2cbfd3e..b7feb15 100644
> > --- a/block/vmdk.c
> > +++ b/block/vmdk.c
> > @@ -556,8 +556,8 @@ static char *vmdk_read_desc(BlockDriverState *file, uint64_t desc_offset,
> >          return NULL;
> >      }
> >  
> > -    size = MIN(size, 1 << 20);  /* avoid unbounded allocation */
> > -    buf = g_malloc0(size + 1);
> > +    size = MIN(size, (1 << 20) - 1);  /* avoid unbounded allocation */
> > +    buf = g_malloc(size + 1);
> >  
> >      ret = bdrv_pread(file, desc_offset, buf, size);
> >      if (ret < 0) {
> > @@ -565,6 +565,7 @@ static char *vmdk_read_desc(BlockDriverState *file, uint64_t desc_offset,
> >          g_free(buf);
> >          return NULL;
> >      }
> > +    buf[ret] = 0;
> >  
> >      return buf;
> >  }
> 

-d
diff mbox

Patch

diff --git a/block/vmdk.c b/block/vmdk.c
index 2cbfd3e..b7feb15 100644
--- a/block/vmdk.c
+++ b/block/vmdk.c
@@ -556,8 +556,8 @@  static char *vmdk_read_desc(BlockDriverState *file, uint64_t desc_offset,
         return NULL;
     }
 
-    size = MIN(size, 1 << 20);  /* avoid unbounded allocation */
-    buf = g_malloc0(size + 1);
+    size = MIN(size, (1 << 20) - 1);  /* avoid unbounded allocation */
+    buf = g_malloc(size + 1);
 
     ret = bdrv_pread(file, desc_offset, buf, size);
     if (ret < 0) {
@@ -565,6 +565,7 @@  static char *vmdk_read_desc(BlockDriverState *file, uint64_t desc_offset,
         g_free(buf);
         return NULL;
     }
+    buf[ret] = 0;
 
     return buf;
 }