How to call sys_link in linux system
This article is to share with you about how to call sys_link in the linux system, the editor thinks it is very practical, so I share it with you to learn. I hope you can get something after reading this article.
Sys_link is a function that creates hard links, and we can see from the code of this function how hard links work. See the previous article for file lookup and manipulation functions. It won't be posted here.
/ / create a hard link
Int sys_link (const char * oldname, const char * newname)
{
Struct dir_entry * de
Struct m_inode * oldinode, * dir
Struct buffer_head * bh
Const char * basename
Int namelen
/ / find the inode node of the file according to the path name
Oldinode=namei (oldname)
If (! oldinode)
Return-ENOENT
/ / hard links cannot be created for directories
If (S_ISDIR (oldinode- > i_mode)) {
/ / No need to use inode, dereference
Iput (oldinode)
Return-EPERM
}
/ / find out the file names in inode and newname of the last level directory of newname
Dir = dir_namei (newname,&namelen,&basename)
/ / the path does not exist
If (! dir) {
Iput (oldinode)
Return-EACCES
}
/ / the path is a directory, so the file name is empty
If (! namelen) {
Iput (oldinode)
Iput (dir)
Return-EPERM
}
/ / hard links cannot be created across file systems
If (dir- > i_dev! = oldinode- > i_dev) {
Iput (dir)
Iput (oldinode)
Return-EXDEV
}
/ / permission verification
If (! permission (dir,MAY_WRITE)) {
Iput (dir)
Iput (oldinode)
Return-EACCES
}
/ / find an item with a file name equal to basename in the directory
Bh = find_entry (& dir,basename,namelen,&de)
/ / if it is found, it means that the file name already exists, then it cannot be created.
If (bh) {
Brelse (bh)
Iput (dir)
Iput (oldinode)
Return-EEXIST
}
/ / if not, a new directory entry is added. De saves the found directory entry.
Bh = add_entry (dir,basename,namelen,&de)
/ / whether the addition is successful
If (! bh) {
Iput (dir)
Iput (oldinode)
Return-ENOSPC
}
/ / the hard-linked inode is the same as the inode number of the old file
De- > inode = oldinode- > i_num
/ / A new item has been added, and the hard disk needs to be written back.
Bh- > b_dirt = 1
Brelse (bh)
Iput (dir)
/ / add 1 to the number of references. Create a hard link and add an index to the inode node, so you can add one to the number of inode references, and only 0 can delete the file.
Oldinode- > iLinklink +
Oldinode- > i_ctime = CURRENT_TIME
/ / the inode information is updated. You need to write back to the hard disk.
Oldinode- > i_dirt = 1
Iput (oldinode)
Return 0
}
The structure is as follows.
The above is how to call sys_link in the linux system. The editor believes that there are some knowledge points that we may see or use in our daily work. I hope you can learn more from this article. For more details, please follow the industry information channel.
