[Xen-devel] [PATCH v3 07/11] igd: revamp host config read

[Gerd Hoffmann <kraxel@xxxxxxxxxx>]

Move all work to the host_pci_config_copy helper function,
which we can easily reuse when adding q35 support.
Open sysfs file only once for all values.  Use pread.
Proper error handling.  Fix bugs:

 * Don't throw away results (like old host_pci_config_read
   did because val was passed by value not reference).
 * Update config space directly (writing via
   pci_default_write_config only works for registers
   whitelisted in wmask).

Hmm, this code can hardly ever worked before,
/me wonders what test coverage it had.

With this patch in place igd-passthru=on actually
works, although it still requires root priviledges
because linux refuses to allow non-root users access
pci config space above offset 0x50.

Signed-off-by: Gerd Hoffmann <kraxel@xxxxxxxxxx>
---
 hw/pci-host/igd.c | 65 +++++++++++++++++++++++--------------------------------
 1 file changed, 27 insertions(+), 38 deletions(-)

diff --git a/hw/pci-host/igd.c b/hw/pci-host/igd.c
index 0784128..ec48875 100644
--- a/hw/pci-host/igd.c
+++ b/hw/pci-host/igd.c
@@ -19,47 +19,39 @@ static const IGDHostInfo igd_host_bridge_infos[] = {
     {0xa8, 4},  /* SNB: base of GTT stolen memory */
 };
 
-static int host_pci_config_read(int pos, int len, uint32_t val)
+static void host_pci_config_copy(PCIDevice *guest, const char *host,
+                                 const IGDHostInfo *list, int len, Error 
**errp)
 {
-    char path[PATH_MAX];
-    int config_fd;
-    ssize_t size = sizeof(path);
-    /* Access real host bridge. */
-    int rc = snprintf(path, size, "/sys/bus/pci/devices/%04x:%02x:%02x.%d/%s",
-                      0, 0, 0, 0, "config");
-    int ret = 0;
+    char *path;
+    int config_fd, rc, i;
 
-    if (rc >= size || rc < 0) {
-        return -ENODEV;
-    }
-
-    config_fd = open(path, O_RDWR);
+    path = g_strdup_printf("/sys/bus/pci/devices/%s/config", host);
+    config_fd = open(path, O_RDONLY);
     if (config_fd < 0) {
-        return -ENODEV;
+        error_setg_file_open(errp, errno, path);
+        goto out_free;
     }
 
-    if (lseek(config_fd, pos, SEEK_SET) != pos) {
-        ret = -errno;
-        goto out;
+    for (i = 0; i < len; i++) {
+        rc = pread(config_fd, guest->config + list[i].offset,
+                   list[i].len, list[i].offset);
+        if (rc != list[i].len) {
+            error_setg_errno(errp, errno, "read %s, offset 0x%x",
+                             path, list[i].offset);
+            goto out_close;
+        }
     }
-    do {
-        rc = read(config_fd, (uint8_t *)&val, len);
-    } while (rc < 0 && (errno == EINTR || errno == EAGAIN));
-    if (rc != len) {
-        ret = -errno;
-    }
-out:
+
+out_close:
     close(config_fd);
-    return ret;
+out_free:
+    g_free(path);
 }
 
 static void (*i440fx_realize)(PCIDevice *pci_dev, Error **errp);
 static void igd_pt_i440fx_realize(PCIDevice *pci_dev, Error **errp)
 {
     Error *err = NULL;
-    uint32_t val = 0;
-    int rc, i, num;
-    int pos, len;
 
     i440fx_realize(pci_dev, &err);
     if (err != NULL) {
@@ -67,16 +59,13 @@ static void igd_pt_i440fx_realize(PCIDevice *pci_dev, Error 
**errp)
         return;
     }
 
-    num = ARRAY_SIZE(igd_host_bridge_infos);
-    for (i = 0; i < num; i++) {
-        pos = igd_host_bridge_infos[i].offset;
-        len = igd_host_bridge_infos[i].len;
-        rc = host_pci_config_read(pos, len, val);
-        if (rc) {
-            error_setg(errp, "failed to read host config");
-            return;
-        }
-        pci_default_write_config(pci_dev, pos, val, len);
+    host_pci_config_copy(pci_dev, "0000:00:00.0",
+                         igd_host_bridge_infos,
+                         ARRAY_SIZE(igd_host_bridge_infos),
+                         &err);
+    if (err != NULL) {
+        error_propagate(errp, err);
+        return;
     }
 }
 
-- 
1.8.3.1


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