2

libfs.c

@@ -1,27 +1,27 @@
-#include <linux/init.h>
 #include <linux/module.h>
 #include <linux/fs.h>
+#include <linux/init.h>
 #include <linux/pagemap.h>
-#include <linux/mount.h>
 #include <linux/namei.h>
+#include <linux/mount.h>
+#include <linux/dcache.h>
 #include <linux/slab.h>
-#include <linux/uaccess.h>
-#include <linux/kernel.h>
 #include <linux/hashtable.h>
-#include <linux/fs_context.h>
+#include <linux/version.h>
-#include <linux/statfs.h>
 
+#define FS_NAME "customfs"
 #define FS_MAGIC 0x20240615
-#define BOOKS_MODE 01777
+#define MODE_BOOKS 01777
-#define AUTHORS_MODE 0777
+#define MODE_AUTHORS 0777
-#define AUTHOR_SUBDIR_MODE 01777
+#define MODE_AUTHOR_SUBDIR 01777
 
 MODULE_LICENSE("GPL");
-MODULE_AUTHOR("user");
+MODULE_AUTHOR("you");
-MODULE_DESCRIPTION("Custom FS with books and authors directories");
+MODULE_DESCRIPTION("Custom FS with books/authors behavior");
 
+static struct super_block *global_sb;
 static struct inode *books_inode;
-static struct inode *authors_inode;
+DEFINE_HASHTABLE(link_table, 6);
 
 struct link_entry {
     struct hlist_node node;
@@ -29,109 +29,31 @@ struct link_entry {
     struct inode *target;
 };
 
-DEFINE_HASHTABLE(link_table, 6);
+static ssize_t dummy_read(struct file *file, char __user *buf, size_t len, loff_t *ppos) {
-
-static void remove_links_to_inode(struct inode *inode) {
-    struct link_entry *entry;
-    struct hlist_node *tmp;
-    int bkt;
-    hash_for_each_safe(link_table, bkt, tmp, entry, node) {
-        if (entry->target == inode) {
-            printk(KERN_INFO "customfs: removing hardlink to inode %lu\n", inode->i_ino);
-            d_delete(entry->link);
-            hash_del(&entry->node);
-            kfree(entry);
-        }
-    }
-}
-
-static void fs_evict_inode(struct inode *inode) {
-    if (inode->i_sb && inode->i_sb->s_magic == FS_MAGIC) {
-        if (S_ISREG(inode->i_mode)) {
-            remove_links_to_inode(inode);
-        }
-    }
-    truncate_inode_pages_final(&inode->i_data);
-    clear_inode(inode);
-}
-
-static int fs_statfs(struct dentry *dentry, struct kstatfs *buf) {
-    buf->f_type = FS_MAGIC;
     return 0;
 }
 
-static const struct super_operations fs_ops = {
+static ssize_t dummy_write(struct file *file, const char __user *buf, size_t len, loff_t *ppos) {
-    .evict_inode = fs_evict_inode,
+    return len;
-    .statfs = fs_statfs,
-};
-
-static ssize_t books_file_read(struct file *file, char __user *buf, size_t len, loff_t *ppos) {
-    return simple_read_from_buffer(buf, len, ppos, file->private_data, PAGE_SIZE);
 }
 
-static ssize_t books_file_write(struct file *file, const char __user *buf, size_t len, loff_t *ppos) {
+static const struct file_operations custom_file_ops = {
-    return simple_write_to_buffer(file->private_data, PAGE_SIZE, ppos, buf, len);
+    .read = dummy_read,
-}
+    .write = dummy_write,
-
+    .llseek = noop_llseek,
-static const struct file_operations books_file_fops = {
-    .read = books_file_read,
-    .write = books_file_write,
-    .llseek = generic_file_llseek,
 };
 
-static const struct inode_operations books_file_iops = {
+static bool is_protected_dentry(struct dentry *d) {
-    .getattr = simple_getattr,
+    return strcmp(d->d_name.name, "books") == 0 || strcmp(d->d_name.name, "authors") == 0;
-    .setattr = simple_setattr,
-};
-
-static const struct inode_operations author_subdir_iops;
-
-static int author_mkdir(struct user_namespace *ns, struct inode *dir, struct dentry *dentry, umode_t mode) {
-    struct inode *inode = new_inode(dir->i_sb);
-    if (!inode)
-        return -ENOMEM;
-    inode->i_ino = get_next_ino();
-    inode_init_owner(&init_user_ns, inode, dir, S_IFDIR | AUTHOR_SUBDIR_MODE);
-    inode->i_op = &author_subdir_iops;
-    inode->i_fop = &simple_dir_operations;
-    inc_nlink(inode);
-    inc_nlink(dir);
-    d_add(dentry, inode);
-    printk(KERN_INFO "customfs: created author subdir '%s'\n", dentry->d_name.name);
-    return 0;
 }
 
-static int author_link(struct dentry *old_dentry, struct inode *dir, struct dentry *new_dentry) {
+static struct inode *get_inode(struct super_block *sb, umode_t mode) {
-    int err;
-    struct inode *inode = d_inode(old_dentry);
-    if (!S_ISREG(inode->i_mode)) return -EPERM;
-    err = simple_link(old_dentry, dir, new_dentry);
-    if (err == 0) {
-        struct link_entry *entry = kmalloc(sizeof(*entry), GFP_KERNEL);
-        if (entry) {
-            entry->link = dget(new_dentry);
-            entry->target = inode;
-            hash_add(link_table, &entry->node, inode->i_ino);
-            printk(KERN_INFO "customfs: created hardlink '%s' to inode %lu\n",
-                   new_dentry->d_name.name, inode->i_ino);
-        }
-    }
-    return err;
-}
-
-static const struct inode_operations author_subdir_iops = {
-    .lookup = simple_lookup,
-    .mkdir = author_mkdir,
-    .rmdir = simple_rmdir,
-    .link = author_link,
-};
-
-static struct inode *fs_make_inode(struct super_block *sb, umode_t mode) {
     struct inode *inode = new_inode(sb);
     if (!inode)
         return NULL;
-    inode->i_ino = get_next_ino();
+
     inode_init_owner(&init_user_ns, inode, NULL, mode);
+    inode->i_ino = get_next_ino();
     inode->i_sb = sb;
     inode->i_atime = inode->i_mtime = inode->i_ctime = current_time(inode);
 
@@ -140,100 +62,178 @@ static struct inode *fs_make_inode(struct super_block *sb, umode_t mode) {
         inode->i_fop = &simple_dir_operations;
         inc_nlink(inode);
     } else if (S_ISREG(mode)) {
-        inode->i_fop = &books_file_fops;
+        inode->i_fop = &custom_file_ops;
-        inode->i_op = &books_file_iops;
-        inode->i_private = kzalloc(PAGE_SIZE, GFP_KERNEL);
     }
     return inode;
 }
 
-static int fs_fill_super(struct super_block *sb, void *data, int silent) {
+static int books_create(struct user_namespace *ns, struct inode *dir,
-    struct inode *root_inode;
+                        struct dentry *dentry, umode_t mode, bool excl) {
-    struct dentry *root_dentry;
+    struct inode *inode = get_inode(dir->i_sb, S_IFREG | mode);
-    struct dentry *books_dentry;
+    if (!inode)
-    struct dentry *authors_dentry;
+        return -ENOMEM;
 
-    sb->s_magic = FS_MAGIC;
+    inode->i_uid = current_fsuid();
-    sb->s_op = &fs_ops;
+    d_add(dentry, inode);
+    return 0;
+}
 
-    root_inode = fs_make_inode(sb, S_IFDIR | 0755);
+static const struct inode_operations books_dir_iops = {
+    .lookup = simple_lookup,
+    .create = books_create,
+};
+
+static void remove_links_to_inode(struct inode *inode) {
+    int bkt;
+    struct link_entry *entry;
+    struct hlist_node *tmp;
+    hash_for_each_safe(link_table, bkt, tmp, entry, node) {
+        if (entry->target == inode) {
+            d_delete(entry->link);
+            dput(entry->link);
+            hash_del(&entry->node);
+            kfree(entry);
+            printk(KERN_INFO "customfs: removed link to inode %lu\n", inode->i_ino);
+        }
+    }
+}
+
+static int custom_mkdir(struct user_namespace *ns, struct inode *dir, struct dentry *dentry, umode_t mode) {
+    if (dir == global_sb->s_root->d_inode)
+        return -EPERM;
+
+    if (S_ISDIR(dir->i_mode)) {
+        umode_t mode_only = dir->i_mode & 07777;
+        if ((mode_only == MODE_AUTHORS || mode_only == MODE_AUTHOR_SUBDIR) &&
+            !uid_eq(current_fsuid(), dir->i_uid))
+            return -EACCES;
+    }
+
+    struct inode *inode = get_inode(dir->i_sb, S_IFDIR | MODE_AUTHOR_SUBDIR);
+    if (!inode)
+        return -ENOMEM;
+
+    inode->i_uid = current_fsuid();
+    d_add(dentry, inode);
+    inc_nlink(dir);
+    return 0;
+}
+
+static int custom_unlink(struct inode *dir, struct dentry *dentry) {
+    if (dir == global_sb->s_root->d_inode && is_protected_dentry(dentry))
+        return -EPERM;
+    return simple_unlink(dir, dentry);
+}
+
+static int custom_rmdir(struct inode *dir, struct dentry *dentry) {
+    if (dir == global_sb->s_root->d_inode && is_protected_dentry(dentry))
+        return -EPERM;
+    return simple_rmdir(dir, dentry);
+}
+
+static int custom_rename(struct user_namespace *ns,
+                         struct inode *old_dir, struct dentry *old_dentry,
+                         struct inode *new_dir, struct dentry *new_dentry,
+                         unsigned int flags) {
+    if ((old_dir == global_sb->s_root->d_inode || new_dir == global_sb->s_root->d_inode) &&
+        (is_protected_dentry(old_dentry) || is_protected_dentry(new_dentry)))
+        return -EPERM;
+    return simple_rename(ns, old_dir, old_dentry, new_dir, new_dentry, flags);
+}
+
+static int custom_link(struct dentry *old_dentry, struct inode *dir, struct dentry *new_dentry) {
+    if (dir->i_sb != old_dentry->d_inode->i_sb)
+        return -EXDEV;
+    if (!S_ISREG(old_dentry->d_inode->i_mode))
+        return -EPERM;
+
+    int r = simple_link(old_dentry, dir, new_dentry);
+    if (r == 0) {
+        struct link_entry *e = kmalloc(sizeof(*e), GFP_KERNEL);
+        if (!e)
+            return -ENOMEM;
+        e->target = d_inode(old_dentry);
+        e->link = dget(new_dentry);
+        hash_add(link_table, &e->node, e->target->i_ino);
+    }
+    return r;
+}
+
+static const struct inode_operations fs_dir_iops = {
+    .lookup = simple_lookup,
+    .mkdir = custom_mkdir,
+    .unlink = custom_unlink,
+    .rmdir = custom_rmdir,
+    .rename = custom_rename,
+    .link = custom_link,
+};
+
+static void evict_inode(struct inode *inode) {
+    if (inode->i_sb == global_sb && inode->i_ino && S_ISREG(inode->i_mode))
+        remove_links_to_inode(inode);
+    clear_inode(inode);
+}
+
+static const struct super_operations fs_sops = {
+    .statfs = simple_statfs,
+    .drop_inode = generic_delete_inode,
+    .evict_inode = evict_inode,
+};
+
+static int fill_super(struct super_block *sb, void *data, int silent) {
+    struct inode *root_inode = get_inode(sb, S_IFDIR | 0755);
     if (!root_inode)
         return -ENOMEM;
 
-    root_dentry = d_make_root(root_inode);
+    struct dentry *root_dentry = d_make_root(root_inode);
     if (!root_dentry)
         return -ENOMEM;
 
-    books_inode = fs_make_inode(sb, S_IFDIR | BOOKS_MODE);
-    if (!books_inode)
-        goto out_root;
-    books_inode->i_op = &simple_dir_inode_operations;
-    books_inode->i_fop = &simple_dir_operations;
-    inc_nlink(books_inode);
-    books_dentry = d_alloc_name(root_dentry, "books");
-    if (!books_dentry)
-        goto out_books;
-    d_add(books_dentry, books_inode);
-    d_rehash(books_dentry);
-    printk(KERN_INFO "customfs: 'books' directory created\n");
-
-    authors_inode = fs_make_inode(sb, S_IFDIR | AUTHORS_MODE);
-    if (!authors_inode)
-        goto out_books_dentry;
-    authors_inode->i_op = &author_subdir_iops;
-    inc_nlink(authors_inode);
-    authors_dentry = d_alloc_name(root_dentry, "authors");
-    if (!authors_dentry)
-        goto out_authors;
-    d_add(authors_dentry, authors_inode);
-    d_rehash(authors_dentry);
-    printk(KERN_INFO "customfs: 'authors' directory created\n");
-
     sb->s_root = root_dentry;
+    sb->s_magic = FS_MAGIC;
+    sb->s_op = &fs_sops;
+    global_sb = sb;
 
-    printk(KERN_INFO "customfs: fill_super completed\n");
+    // books
-    printk(KERN_INFO "customfs: root inode=%lu\n", root_inode->i_ino);
+    books_inode = get_inode(sb, S_IFDIR | MODE_BOOKS);
-    printk(KERN_INFO "customfs: books inode=%lu\n", books_inode->i_ino);
+    if (!books_inode)
-    printk(KERN_INFO "customfs: authors inode=%lu\n", authors_inode->i_ino);
+        return -ENOMEM;
+    books_inode->i_op = &books_dir_iops;
+    books_inode->i_fop = &simple_dir_operations;
+    struct dentry *books = d_alloc_name(root_dentry, "books");
+    d_add(books, books_inode);
+
+    // authors
+    struct inode *authors_inode = get_inode(sb, S_IFDIR | MODE_AUTHORS);
+    if (!authors_inode)
+        return -ENOMEM;
+    authors_inode->i_op = &fs_dir_iops;
+    authors_inode->i_fop = &simple_dir_operations;
+    struct dentry *authors = d_alloc_name(root_dentry, "authors");
+    d_add(authors, authors_inode);
 
     return 0;
-
-out_authors:
-    iput(authors_inode);
-out_books_dentry:
-    dput(books_dentry);
-out_books:
-    iput(books_inode);
-out_root:
-    dput(root_dentry);
-    iput(root_inode);
-    return -ENOMEM;
 }
 
-static struct dentry *fs_mount(struct file_system_type *type, int flags,
+static struct dentry *mount_fs(struct file_system_type *type, int flags, const char *dev, void *data) {
-                               const char *dev, void *data) {
+    return mount_nodev(type, flags, data, fill_super);
-    printk(KERN_INFO "customfs: mounting\n");
-    return mount_nodev(type, flags, data, fs_fill_super);
 }
 
 static struct file_system_type fs_type = {
     .owner = THIS_MODULE,
-    .name = "customfs",
+    .name = FS_NAME,
-    .mount = fs_mount,
+    .mount = mount_fs,
     .kill_sb = kill_litter_super,
 };
 
 static int __init fs_init(void) {
     hash_init(link_table);
-    printk(KERN_INFO "customfs: module loaded\n");
     return register_filesystem(&fs_type);
 }
 
 static void __exit fs_exit(void) {
     unregister_filesystem(&fs_type);
-    printk(KERN_INFO "customfs: module unloaded\n");
 }
 
 module_init(fs_init);
 module_exit(fs_exit);
-

t.bash

@@ -0,0 +1,14 @@
+#!/bin/bash
+
+# создать файл
+echo test > /mnt/customfs/books/hello.txt
+
+# создать подкаталог
+mkdir /mnt/customfs/authors/kirill
+
+# создать жёсткую ссылку
+ln /mnt/customfs/books/hello.txt /mnt/customfs/authors/kirill/hlink
+
+# удалить исходный файл
+rm /mnt/customfs/books/hello.txt
+# => ссылка в authors также исчезнет