Xen devel - Jan 2012 - [PATCH] qemu-xen: fix sequence of operations in pt_msix_init()

Checking the return value of mmap() must be done before adjusting the
value, otherwise failure may not be detected.

Closing the file handle, on the other hand, can be done before checking
the return value.

Finally, printing the errno value without knowing whether the previous
function actually failed is bogus (and superfluous since a subsequent
message prints the strerror() representaton anyway).

Signed-off-by: Jan Beulich <jbeulich@suse.com>

--- a/hw/pt-msi.c
+++ b/hw/pt-msi.c
@@ -537,7 +537,6 @@ int pt_msix_init(struct pt_dev *dev, int
     int i, total_entries, table_off, bar_index;
     struct pci_dev *pd = dev->pci_dev;
     int fd;
-    int err;
 
     id = pci_read_byte(pd, pos + PCI_CAP_LIST_ID);
 
@@ -585,17 +584,14 @@ int pt_msix_init(struct pt_dev *dev, int
     dev->msix->phys_iomem_base = mmap(0, total_entries * 16 +
dev->msix->table_offset_adjust,
                           PROT_READ, MAP_SHARED | MAP_LOCKED,
                           fd, dev->msix->table_base + table_off -
dev->msix->table_offset_adjust);
-    dev->msix->phys_iomem_base = (void *)((char
*)dev->msix->phys_iomem_base +
-                          dev->msix->table_offset_adjust);
-    err = errno;
-    PT_LOG("errno = %d\n",err);
+    close(fd);
     if ( dev->msix->phys_iomem_base == MAP_FAILED )
     {
         PT_LOG("Error: Can''t map physical MSI-X table:
%s\n", strerror(errno));
-        close(fd);
         goto error_out;
     }
-    close(fd);
+
+    dev->msix->phys_iomem_base += dev->msix->table_offset_adjust;
 
     PT_LOG("mapping physical MSI-X table to %lx\n",
            (unsigned long)dev->msix->phys_iomem_base);





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On Tue, 3 Jan 2012, Jan Beulich wrote:
> Checking the return value of mmap() must be done before adjusting the
> value, otherwise failure may not be detected.
> 
> Closing the file handle, on the other hand, can be done before checking
> the return value.
> 
> Finally, printing the errno value without knowing whether the previous
> function actually failed is bogus (and superfluous since a subsequent
> message prints the strerror() representaton anyway).
> 
> Signed-off-by: Jan Beulich <jbeulich@suse.com>
acked

Stefano Stabellini writes ("Re: [Xen-devel] [PATCH] qemu-xen: fix sequence
of operations in pt_msix_init()"):
> On Tue, 3 Jan 2012, Jan Beulich wrote:
> > Checking the return value of mmap() must be done before adjusting the
> > value, otherwise failure may not be detected.
> > 
> > Closing the file handle, on the other hand, can be done before
checking
> > the return value.
> > 
> > Finally, printing the errno value without knowing whether the previous
> > function actually failed is bogus (and superfluous since a subsequent
> > message prints the strerror() representaton anyway).
> > 
> > Signed-off-by: Jan Beulich <jbeulich@suse.com>
> 
> acked
Committed-by: Ian Jackson <ian.jackson@eu.citrix.com>