xenforeignmemory: work around bug in older privcmd

Versions of linux privcmd prior to commit dc9eab6fd94d ("return -ENOTTY
for unimplemented IOCTLs") will return -EINVAL rather than the conventional
-ENOTTY for unimplemented codes. This breaks the error path in
libxenforeignmemory resource mapping, which only translates ENOTTY into
EOPNOTSUPP to inform callers of the need to use an alternative (legacy)
mechanism.

This patch adds a new 'unimplemented' [1] ioctl code into the local
privcmd header which is then used to probe for the appropriate errno to
translate in the resource mapping error path

[1] this is a code that has, so far, never been used in any version of
    privcmd and will be added to future versions of the header in the
    linux source, to make sure it stays unimplemented.

Signed-off-by: Paul Durrant <paul.durrant@citrix.com>
Acked-by: Wei Liu <wei.liu2@citrix.com>
Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>

diff --git a/tools/include/xen-sys/Linux/privcmd.h b/tools/include/xen-sys/Linux/privcmd.h
index 9531b728f9cb6db3f44d3343a05eba6066ec65c2..bc60e8fd55ebcc687f33d7d9ae06e360a78d9fd9 100644 (file)
--- a/tools/include/xen-sys/Linux/privcmd.h
+++ b/tools/include/xen-sys/Linux/privcmd.h
@@ -114,5 +114,7 @@ typedef struct privcmd_mmap_resource {
        _IOC(_IOC_NONE, 'P', 6, sizeof(domid_t))
 #define IOCTL_PRIVCMD_MMAP_RESOURCE                            \
        _IOC(_IOC_NONE, 'P', 7, sizeof(privcmd_mmap_resource_t))
+#define IOCTL_PRIVCMD_UNIMPLEMENTED                            \
+       _IOC(_IOC_NONE, 'P', 0xFF, 0)
 
 #endif /* __LINUX_PUBLIC_PRIVCMD_H__ */

diff --git a/tools/libs/foreignmemory/linux.c b/tools/libs/foreignmemory/linux.c
index 3686cf41e054399903bd2a09be620c60bc5e6a8f..0368aa09f4c892310dccc10f543441353049433a 100644 (file)
--- a/tools/libs/foreignmemory/linux.c
+++ b/tools/libs/foreignmemory/linux.c
@@ -53,6 +53,23 @@ int osdep_xenforeignmemory_open(xenforeignmemory_handle *fmem)
         return -1;
     }
 
+    /*
+     * Older versions of privcmd return -EINVAL for unimplemented ioctls
+     * so we need to probe for the errno to use rather than just using
+     * the conventional ENOTTY.
+     */
+    if ( ioctl(fd, IOCTL_PRIVCMD_UNIMPLEMENTED, NULL) >= 0 )
+    {
+        xtl_log(fmem->logger, XTL_ERROR, -1, "xenforeignmemory",
+                "privcmd ioctl should not be implemented");
+        return -1;
+    }
+    else
+    {
+        fmem->unimpl_errno = errno;
+        errno = 0;
+    }
+
     fmem->fd = fd;
     return 0;
 }
@@ -307,7 +324,7 @@ int osdep_xenforeignmemory_map_resource(
     {
         int saved_errno;
 
-        if ( errno != ENOTTY && errno != EOPNOTSUPP )
+        if ( errno != fmem->unimpl_errno && errno != EOPNOTSUPP )
             PERROR("ioctl failed");
         else
             errno = EOPNOTSUPP;

diff --git a/tools/libs/foreignmemory/private.h b/tools/libs/foreignmemory/private.h
index b06ce12583fa62ec7df8593b22ffc740e24b2859..8f1bf081ed9083a7887aaa858f873baea62475c3 100644 (file)
--- a/tools/libs/foreignmemory/private.h
+++ b/tools/libs/foreignmemory/private.h
@@ -23,6 +23,7 @@ struct xenforeignmemory_handle {
     unsigned flags;
     int fd;
     Xentoolcore__Active_Handle tc_ah;
+    int unimpl_errno;
 };
 
 int osdep_xenforeignmemory_open(xenforeignmemory_handle *fmem);