[PATCH] [sysfs]: make readlink result shorter when the symlink and its target shared some base sysfs subdirectory

[Denis Cheng]

this is especially useful after /sys/slab introduced, for example:

$ ls -l /sys/slab/mm_struct
lrwxrwxrwx 1 root root 0 2007-10-31 17:40 /sys/slab/mm_struct -> :0000448

instead of:

$ ls -l /sys/slab/mm_struct
lrwxrwxrwx 1 root root 0 2007-10-31 17:40 /sys/slab/mm_struct -> 
../slab/:0000448

Signed-off-by: Denis Cheng <[EMAIL PROTECTED]>
---
 fs/sysfs/symlink.c |   38 +++++++++++++++++++++++++++-----------
 1 files changed, 27 insertions(+), 11 deletions(-)

diff --git a/fs/sysfs/symlink.c b/fs/sysfs/symlink.c
index 3eac20c..230a925 100644
--- a/fs/sysfs/symlink.c
+++ b/fs/sysfs/symlink.c
@@ -19,30 +19,41 @@
 
 #include "sysfs.h"
 
-static int object_depth(struct sysfs_dirent *sd)
+static struct sysfs_dirent *object_base(struct sysfs_dirent *parent,
+               struct sysfs_dirent *sd)
+{
+       for (; sd->s_parent; sd = sd->s_parent)
+               if (sd->s_parent == parent)
+                       return parent;
+       return NULL;
+}
+
+static int object_depth(struct sysfs_dirent *base, struct sysfs_dirent *sd)
 {
        int depth = 0;
 
-       for (; sd->s_parent; sd = sd->s_parent)
+       for (; sd->s_parent && sd != base; sd = sd->s_parent)
                depth++;
 
        return depth;
 }
 
-static int object_path_length(struct sysfs_dirent * sd)
+static int object_path_length(struct sysfs_dirent *base,
+               struct sysfs_dirent *sd)
 {
        int length = 1;
 
-       for (; sd->s_parent; sd = sd->s_parent)
+       for (; sd->s_parent && sd != base; sd = sd->s_parent)
                length += strlen(sd->s_name) + 1;
 
        return length;
 }
 
-static void fill_object_path(struct sysfs_dirent *sd, char *buffer, int length)
+static void fill_object_path(struct sysfs_dirent *base,
+               struct sysfs_dirent *sd, char *buffer, int length)
 {
        --length;
-       for (; sd->s_parent; sd = sd->s_parent) {
+       for (; sd->s_parent && sd != base; sd = sd->s_parent) {
                int cur = strlen(sd->s_name);
 
                /* back up enough to print this bus id with '/' */
@@ -129,18 +140,23 @@ static int sysfs_get_target_path(struct sysfs_dirent * 
parent_sd,
 {
        char * s;
        int depth, size;
+       struct sysfs_dirent *base;
 
-       depth = object_depth(parent_sd);
-       size = object_path_length(target_sd) + depth * 3 - 1;
+       base = object_base(parent_sd, target_sd);
+       depth = object_depth(base, parent_sd);
+       size = object_path_length(base, target_sd) + depth * 3 - 1;
        if (size > PATH_MAX)
                return -ENAMETOOLONG;
 
-       pr_debug("%s: depth = %d, size = %d\n", __FUNCTION__, depth, size);
+       pr_debug("%s: base = %s, depth = %d, size = %d\n",
+                       __FUNCTION__,
+                       base ? base->s_name : "/sys",
+                       depth, size);
 
        for (s = path; depth--; s += 3)
-               strcpy(s,"../");
+               strcpy(s, "../");
 
-       fill_object_path(target_sd, path, size);
+       fill_object_path(base, target_sd, path, size);
        pr_debug("%s: path = '%s'\n", __FUNCTION__, path);
 
        return 0;
-- 
1.5.3.4

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