Chapter 10: Filesystems without Persistent Storage
entry->write_proc = hypercard_proc_write;
}Once the entry has been created, it is registered with theprocfilesystem usingproc_registerin
fs/proc/generic.c. The task is divided into three steps:
- Auniqueproc-internal number is generated to give the entry its own identity.
get_inode_numberis used to return an unused number for dynamically generated
entries. - Thenextandparentelements of theproc_dir_entryinstance must be set appropriately to
incorporate the new entry into the hierarchy. - Depending on the file type, the pointers must be set appropriately to file and inode
operations if the corresponding elements ofproc_dir_entry,proc_iopsandproc_fops
previously contained a null pointer. Otherwise, the value held there is retained.
Which file and inode operations are used forprocfiles? The corresponding pointers are set as
follows:
fs/proc/generic.c
static int proc_register(struct proc_dir_entry * dir, struct proc_dir_entry * dp)
{
if (S_ISDIR(dp->mode)) {
if (dp->proc_iops == NULL) {
dp->proc_fops = &proc_dir_operations;
dp->proc_iops = &proc_dir_inode_operations;
}
dir->nlink++;
} else if (S_ISLNK(dp->mode)) {
if (dp->proc_iops == NULL)
dp->proc_iops = &proc_link_inode_operations;
} else if (S_ISREG(dp->mode)) {
if (dp->proc_fops == NULL)
dp->proc_fops = &proc_file_operations;
if (dp->proc_iops == NULL)
dp->proc_iops = &proc_file_inode_operations;
}
...
}For regular files, the kernel usesproc_file_operationsandproc_file_inode_operationsto define
the file and inode operation methods:
fs/proc/generic.c
static struct inode_operations proc_file_inode_operations = {
.setattr = proc_notify_change,
};fs/proc/generic.c
static struct file_operations proc_file_operations = {
.llseek = proc_file_lseek,
.read = proc_file_read,
.write = proc_file_write,
};