Linux file System (ii)-Virtual file system __linux

The

Virtual file system layer provides most of the functions like vfs_xxx, and they end up calling the struct inode_operations and struct of the virtual file system that each specific file system is registered to File_ Some operation functions in operations and other structure bodies. Take the FAT file system as an example, he registered struct inode_operations and struct file_operations as follows:

fs/fat/namei_vfat.c
static const struct Inode_operations vfat_dir_inode_operations = {
        . Create         = Vfat_ Create,
        . Lookup         = vfat_lookup,
        . Unlink         = Vfat_unlink,
        . mkdir          = Vfat_mkdir,
        . rmdir          = Vfat_rmdir,
        . Rename         = Vfat_rename,
        . SetAttr        = fat_setattr,
        . getattr        = Fat_ GetAttr,
};

fs/fat/file.c
const struct File_operations fat_file_operations = {
        . Llseek         = Generic_file_llseek,
        . Read           = Do_sync_read,
        . Write          = Do_sync_write,
        . Aio_read       = Generic_file_aio_read,
        . Aio_write      = Generic_file_aio_write,
        . mmap           = Generic_file_mmap,
        . Release        = Fat_ File_release,
        . Unlocked_ioctl = Fat_generic_ioctl,
        . Fsync          = Fat_file_fsync,
        . Splice_read    = Generic_file_splice_read,
};

Open System Call

FS/OPEN.C
syscall_define3 (open, const char __user *, filename, ...)
    Do_sys_open
        do_filp_open//fs/namei.c
            path_openat
                do_last
                    lookup_open
                        Finish _open
                            do_dentry_open
                                f->f_op = Fops_get (INODE->I_FOP);

In the open, the structure in the inode is struct file_operations i_fop the stored function pointer to the structure in file struct file_operations f_op, later read, Functions called write and so on are the callback functions in the struct file_operations structure here. Write system call

fs/read_write.c
syscall_define3 (write, ...
    ) Vfs_write
        file->f_op->write (FAT file system is Do_sync_write)
        do_sync_write
            filp->f_op->aio_write (FAT file system is Generic_file_aio_write)
            Generic_file_aio_write//mm/filemap.c
                __generic_file_aio_write
                    generic_file_buffered_write
                        generic_ Perform_write
                            a_ops->write_begin
                            iov_iter_copy_from_user_atomic
                            a_ops->write_end

First, system call write calls the function in the virtual file system Vfs_write,vfs_write will eventually call the F_op->aio_write function in the struct file_operations function that the FAT file system registers. Generic_file_aio_write is a function implemented in a MM/FILEMAP.C file that writes data to the page cache and waits for the write-back thread to write page cache to disk. mkdir system Call

FS/NAMEI.C
syscall_define2 (mkdir, ...
    Sys_mkdirat
syscall_define3 (Mkdirat, ...
    Vfs_mkdir (struct inode *dir, struct dentry *dentry, ...)
        Dir->i_op->mkdir

mkdir system calls are not the same as write system calls, he calls functions in the struct inode_operations structure in the inode, and the write system calls the struct in file File_ Operations the function in the structure body.