linux-kernel - linux 内核中的 path_lookup 如何工作？

Question

我们是否需要提供完整路径或仅提供对象名称(文件/目录)，它是否处理路径中的挂载目录以及 LOOKUP_FOLLOW 是什么意思？

Answer 1

您可能知道，path_lookup 用于查找与路径名字符串对应的目录。搜索将按以下方式进行:

245      dentry 0
246     +---------------------+   rcu-walk begins here, we note d_seq, check the
247     | name:    "/"        |   inode's permission, and then look up the next
248     | inode:   10         |   path element which is "home"...
249     | children:"home", ...|
250     +---------------------+
251               |
252      dentry 1 V
253     +---------------------+   ... which brings us here. We find dentry1 via
254     | name:    "home"     |   hash lookup, then note d_seq and compare name
255     | inode:   678        |   string and parent pointer. When we have a match,
256     | children:"npiggin"  |   we now recheck the d_seq of dentry0. Then we
257     +---------------------+   check inode and look up the next element.
258               |
259      dentry2  V
260     +---------------------+   Note: if dentry0 is now modified, lookup is
261     | name:    "npiggin"  |   not necessarily invalid, so we need only keep a
262     | inode:   543        |   parent for d_seq verification, and grandparents
263     | children:"a.c", ... |   can be forgotten.
264     +---------------------+
265               |
266      dentry3  V
267     +---------------------+   At this point we have our destination dentry.
268     | name:    "a.c"      |   We now take its d_lock, verify d_seq of this
269     | inode:   14221      |   dentry. If that checks out, we can increment
270     | children:NULL       |   its refcount because we're holding d_lock.

所以问题第一部分的答案是——应该指定完整路径。关于 LOOKUP_FOLLOW - 如果指定，它将在搜索期间遵循符号链接(symbolic link)。

Does it take care of mounted directory in the path

不知道你在这里是什么意思。

详情请见: http://www2.comp.ufscar.br/lxr/source/Documentation/filesystems/path-lookup.txt?a=ia64