关于sysfs的几个问题
最近在看sysfs相关的代码，但有些地方不是很清楚，下面是发到linux-kernel的两封邮件，但一直没有回复（难道我做什么不礼貌了？），也过来这边请教一下大家。Hi,
I found the initialization code of the sysfs in version 2.6.22:
int __init sysfs_init(void)
{
int err = -ENOMEM;
sysfs_dir_cachep = kmem_cache_create("sysfs_dir_cache",
sizeof(struct sysfs_dirent),
0, 0, NULL, NULL);
if (!sysfs_dir_cachep)
goto out;
err = register_filesystem(&sysfs_fs_type);
if (!err) {
sysfs_mount = kern_mount(&sysfs_fs_type);
........
my questions are:
1. Is some initializing script responsible for mounting the sysfs? If
so, why do we call kern_mount.
2. I looked into the kern_mount code, the routine seems to get the
super block and the inode object for the sysfs, but when setting the
root, I got:
root = d_alloc_root(inode);
if (!root) {
pr_debug("%s: could not get root dentry!\n",__FUNCTION__);
iput(inode);
return -ENOMEM;
}
root->d_fsdata = &sysfs_root;
sb->s_root = root;
and the s_root is then passed to the mnt_root and the mnt_mountpoint:
int simple_set_mnt(struct vfsmount *mnt, struct super_block *sb)
{
mnt->mnt_sb = sb;
mnt->mnt_root = dget(sb->s_root);
return 0;
}
in vfs_kern_mount:
.......
mnt->mnt_mountpoint = mnt->mnt_root;
mnt->mnt_parent = mnt;
up_write(&mnt->mnt_sb->s_umount);
.......
So, does this means we get the mount point from d_alloc_root(inode),
but this doesn't look like the truth. d_alloc_root seems to allocate a
dentry for the root, is that true? If so, why for the root?
Does the s_root stand for the root of the file system, so it should
always be "/", but this is different from root file system? But what
about the mnt_moountpoint, how does the kernel store the path (rooted
from theroot file system)?
Thanks
Hi all,
Currently, I'm studying the code of the sysfs. But I got the
following questions:
1. What is the d_alloc_root used for? Actually, the question should
be: why we have to call d_alloc_root. I think the root already has its
dentry, why we have to allocate another while we mounting a file
system?
2. Why we call d_alloc_root to allocate a dentry for the mount point
while the usual mount point of sysfs is defined by the user (something
like /sysfs but not /). See below:
root = d_alloc_root(inode);
if (!root) {
pr_debug("%s: could not get root dentry!\n",__FUNCTION__);
iput(inode);
return -ENOMEM;
}
root->d_fsdata = &sysfs_root;
sb->s_root = root;
does this means settting the sysfs' mount point to "/" but not "/sysfs".
Thanks.
先谢谢大家
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