optimize sysfs device and attribute cache

Add negative cache for attributes and look for device in cache before doing
any sysfs access. (Three times speed up for a stupid 1000 rules SYSFS file).

Signed-off-by: Kay Sievers <kay.sievers@suse.de>

diff --git a/udev.h b/udev.h
index 0c7ca12f10def122a55a8359cc2968df491e2910..2652d46ada8d4db45052aa7ed16f8d4c6674dec5 100644 (file)
--- a/udev.h
+++ b/udev.h
@@ -54,6 +54,7 @@ struct udev_rules;
 
 struct sysfs_device {
        struct list_head node;                  /* for device cache */
+       struct sysfs_device *parent;            /* already cached parent*/
        char devpath[PATH_SIZE];
        char subsystem[NAME_SIZE];              /* $class/$bus/"drivers" */
        char kernel_name[NAME_SIZE];            /* device instance name */

diff --git a/udev_sysfs.c b/udev_sysfs.c
index 8de523dadf66abc3bbf0198c9dac01036ca7f608..b579c17caab8a8318ad82a25d37d499c7114981d 100644 (file)
--- a/udev_sysfs.c
+++ b/udev_sysfs.c
@@ -40,7 +40,8 @@ static LIST_HEAD(attr_list);
 struct sysfs_attr {
        struct list_head node;
        char path[PATH_SIZE];
-       char value[NAME_SIZE];
+       char *value;                    /* points to value_local if value is cached */
+       char value_local[NAME_SIZE];
 };
 
 int sysfs_init(void)
@@ -126,14 +127,21 @@ struct sysfs_device *sysfs_device_get(const char *devpath)
        strlcpy(devpath_real, devpath, sizeof(devpath_real));
        remove_trailing_chars(devpath_real, '/');
 
+       /* look for device already in cache (we never put an untranslated path in the cache) */
+       list_for_each_entry(dev_loop, &dev_list, node) {
+               if (strcmp(dev_loop->devpath, devpath_real) == 0) {
+                       dbg("found in cache '%s'", dev_loop->devpath);
+                       return dev_loop;
+               }
+       }
+
+       /* if we got a link, resolve it to the real device */
        strlcpy(path, sysfs_path, sizeof(path));
        strlcat(path, devpath_real, sizeof(path));
        if (lstat(path, &statbuf) != 0) {
                dbg("stat '%s' failed: %s", path, strerror(errno));
                return NULL;
        }
-
-       /* if we got a link, resolve it to the real device */
        if (S_ISLNK(statbuf.st_mode)) {
                int i;
                int back;
@@ -156,17 +164,17 @@ struct sysfs_device *sysfs_device_get(const char *devpath)
                dbg("after moving back '%s'", devpath_real);
                strlcat(devpath_real, "/", sizeof(devpath_real));
                strlcat(devpath_real, &link_target[back * 3], sizeof(devpath_real));
-       }
 
-       /* look for device in cache */
-       list_for_each_entry(dev_loop, &dev_list, node) {
-               if (strcmp(dev_loop->devpath, devpath_real) == 0) {
-                       dbg("found in cache '%s'", dev_loop->devpath);
-                       return dev_loop;
+               /* now look for device in cache after path translation */
+               list_for_each_entry(dev_loop, &dev_list, node) {
+                       if (strcmp(dev_loop->devpath, devpath_real) == 0) {
+                               dbg("found in cache '%s'", dev_loop->devpath);
+                               return dev_loop;
+                       }
                }
        }
 
-       /* new device */
+       /* it is a new device */
        dbg("'%s'", devpath_real);
        dev = malloc(sizeof(struct sysfs_device));
        if (dev == NULL)
@@ -245,6 +253,9 @@ struct sysfs_device *sysfs_device_get_parent(struct sysfs_device *dev)
        int len;
        int back;
 
+       if (dev->parent != NULL)
+               return dev->parent;
+
        /* requesting a parent is only valid for devices */
        if ((strncmp(dev->devpath, "/devices/", 9) != 0) &&
            (strncmp(dev->devpath, "/class/", 7) != 0) &&
@@ -266,12 +277,11 @@ struct sysfs_device *sysfs_device_get_parent(struct sysfs_device *dev)
                return NULL;
        }
 
-       /* at the top level we may follow the "device" link */
+       /* at the top level of class/block we want to follow the "device" link */
        if (strcmp(parent_devpath, "/block") == 0) {
                dbg("/block top level, look for device link");
                goto device_link;
        }
-
        if (strncmp(parent_devpath, "/class", 6) == 0) {
                pos = strrchr(parent_devpath, '/');
                if (pos == &parent_devpath[6] || pos == parent_devpath) {
@@ -279,7 +289,8 @@ struct sysfs_device *sysfs_device_get_parent(struct sysfs_device *dev)
                        goto device_link;
                }
        }
-       return sysfs_device_get(parent_devpath);
+       dev->parent = sysfs_device_get(parent_devpath);
+       return dev->parent;
 
 device_link:
        strlcpy(device_link, sysfs_path, sizeof(device_link));
@@ -304,7 +315,9 @@ device_link:
        dbg("after moving back '%s'", parent_devpath);
        strlcat(parent_devpath, "/", sizeof(parent_devpath));
        strlcat(parent_devpath, &device_link_target[back * 3], sizeof(parent_devpath));
-       return sysfs_device_get(parent_devpath);
+
+       dev->parent = sysfs_device_get(parent_devpath);
+       return dev->parent;
 }
 
 struct sysfs_device *sysfs_device_get_parent_with_subsystem(struct sysfs_device *dev, const char *subsystem)
@@ -345,27 +358,32 @@ char *sysfs_attr_get_value(const char *devpath, const char *attr_name)
                }
        }
 
+       /* store attribute in cache (also negatives are kept in cache) */
+       attr = malloc(sizeof(struct sysfs_attr));
+       if (attr == NULL)
+               return NULL;
+       memset(attr, 0x00, sizeof(struct sysfs_attr));
+       strlcpy(attr->path, path, sizeof(attr->path));
+       dbg("add to cache '%s' '%s'", attr->path, attr->value);
+       list_add(&attr->node, &attr_list);
+
        /* read attribute value */
        fd = open(path_full, O_RDONLY);
        if (fd < 0)
-               return NULL;
+               goto out;
        size = read(fd, value, sizeof(value));
        close(fd);
        if (size < 0)
-               return NULL;
+               goto out;
        if (size == sizeof(value))
-               return NULL;
+               goto out;
+
+       /* got a valid value, store and return it */
        value[size] = '\0';
        remove_trailing_chars(value, '\n');
+       strlcpy(attr->value_local, value, sizeof(attr->value_local));
+       attr->value = attr->value_local;
 
-       /* store attribute in cache */
-       attr = malloc(sizeof(struct sysfs_attr));
-       if (attr == NULL)
-               return NULL;
-       strlcpy(attr->path, path, sizeof(attr->path));
-       strlcpy(attr->value, value, sizeof(attr->value));
-       dbg("add to cache '%s' '%s'", attr->path, attr->value);
-       list_add(&attr->node, &attr_list);
-
+out:
        return attr->value;
 }