linux: Switch to kernel version check to determine if sysfs has descriptors

With the refactoring of the Linux descriptors handling, we only want to use
sysfs descriptors if they have the complete config descriptors (versus just
the active config descriptor), which is the case since Linux 2.6.26.

This means that we will fallback to using the usbfs descriptors for the device
descriptor on Linux 2.6.23 - 2.6.25, which only have the active config
descriptor. This will cause a tiny performance penalty, but only on these
3 kernel versions (which are not used in any still supported Linux distros),
and then only on library init since we now cache everything.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>

diff --git a/libusb/os/linux_usbfs.c b/libusb/os/linux_usbfs.c
index 9c07549..5b7cf40 100644 (file)
--- a/libusb/os/linux_usbfs.c
+++ b/libusb/os/linux_usbfs.c
@@ -46,7 +46,11 @@
  *
  * sysfs allows us to read the kernel's in-memory copies of device descriptors
  * and so forth, avoiding the need to open the device:
- *  - The binary "descriptors" file was added in 2.6.23.
+ *  - The binary "descriptors" file contains all config descriptors since
+ *    2.6.26, commit 217a9081d8e69026186067711131b77f0ce219ed 
+ *  - The binary "descriptors" file was added in 2.6.23, commit
+ *    69d42a78f935d19384d1f6e4f94b65bb162b36df, but it only contains the
+ *    active config descriptors
  *  - The "busnum" file was added in 2.6.22
  *  - The "devnum" file has been present since pre-2.6.18
  *  - the "bConfigurationValue" file has been present since pre-2.6.18
@@ -57,12 +61,8 @@
  * The busnum file is important as that is the only way we can relate sysfs
  * devices to usbfs nodes.
  *
- * If we also have descriptors, we can obtain the device descriptor and active 
+ * If we also have all descriptors, we can obtain the device descriptor and
  * configuration without touching usbfs at all.
- *
- * The descriptors file originally only contained the active configuration
- * descriptor alongside the device descriptor, but all configurations are
- * included as of Linux 2.6.26.
  */
 
 /* endianness for multi-byte fields:
@@ -70,6 +70,8 @@
  * Descriptors exposed by usbfs have the multi-byte fields in the device
  * descriptor as host endian. Multi-byte fields in the other descriptors are
  * bus-endian. The kernel documentation says otherwise, but it is wrong.
+ *
+ * In sysfs all descriptors are bus-endian.
  */
 
 static const char *usbfs_path = NULL;
@@ -108,8 +110,10 @@ static clockid_t monotonic_clkid = -1;
  * the active configuration through bConfigurationValue */
 static int sysfs_can_relate_devices = 0;
 
-/* do we have a descriptors file? */
-static int sysfs_has_descriptors = 0;
+/* Linux 2.6.26 (commit 217a9081d8e69026186067711131b77f0ce219ed) adds all
+ * config descriptors (rather then just the active config) to the sysfs
+ * descriptors file, so from then on we can use them. */
+static int sysfs_has_descriptors = -1;
 
 /* how many times have we initted (and not exited) ? */
 static volatile int init_count = 0;
@@ -395,6 +399,15 @@ static int op_init(struct libusb_context *ctx)
        if (supports_flag_zero_packet)
                usbi_dbg("zero length packet flag supported");
 
+       if (-1 == sysfs_has_descriptors) {
+               /* sysfs descriptors has all descriptors since Linux 2.6.26 */
+               sysfs_has_descriptors = kernel_version_ge(2,6,26);
+               if (-1 == sysfs_has_descriptors) {
+                       usbi_err(ctx, "error checking for sysfs descriptors");
+                       return LIBUSB_ERROR_OTHER;
+               }
+       }
+
        r = stat(SYSFS_DEVICE_PATH, &statbuf);
        if (r == 0 && S_ISDIR(statbuf.st_mode)) {
                DIR *devices = opendir(SYSFS_DEVICE_PATH);
@@ -422,7 +435,7 @@ static int op_init(struct libusb_context *ctx)
                 * See the "sysfs vs usbfs" comment at the top of this file
                 * for more details.  */
                while ((entry = readdir(devices))) {
-                       int has_busnum=0, has_devnum=0, has_descriptors=0;
+                       int has_busnum=0, has_devnum=0;
                        int has_configuration_value=0;
 
                        /* Only check the usbN directories. */
@@ -432,25 +445,14 @@ static int op_init(struct libusb_context *ctx)
                        /* Check for the files libusbx needs from sysfs. */
                        has_busnum = sysfs_has_file(entry->d_name, "busnum");
                        has_devnum = sysfs_has_file(entry->d_name, "devnum");
-                       has_descriptors = sysfs_has_file(entry->d_name, "descriptors");
                        has_configuration_value = sysfs_has_file(entry->d_name, "bConfigurationValue");
 
-                       if (has_busnum && has_devnum && has_configuration_value)
+                       if (has_busnum && has_devnum && has_configuration_value) {
                                sysfs_can_relate_devices = 1;
-                       if (has_descriptors)
-                               sysfs_has_descriptors = 1;
-
-                       /* Only need to check until we've found ONE device which
-                          has all the attributes. */
-                       if (sysfs_has_descriptors && sysfs_can_relate_devices)
                                break;
+                       }
                }
                closedir(devices);
-
-               /* Only use sysfs descriptors if the rest of
-                  sysfs will work for libusb. */
-               if (!sysfs_can_relate_devices)
-                       sysfs_has_descriptors = 0;
        } else {
                usbi_dbg("sysfs usb info not available");
                sysfs_has_descriptors = 0;

diff --git a/libusb/version_nano.h b/libusb/version_nano.h
index 044b0da..27ae94c 100644 (file)
--- a/libusb/version_nano.h
+++ b/libusb/version_nano.h
@@ -1 +1 @@
-#define LIBUSB_NANO 10703
+#define LIBUSB_NANO 10704