FreeBSD/Linux Kernel Cross Reference
sys/fs/file_table.c

     /*
      *  linux/fs/file_table.c
      *
      *  Copyright (C) 1991, 1992  Linus Torvalds
      *  Copyright (C) 1997 David S. Miller (davem@caip.rutgers.edu)
      */
     
     #include <linux/string.h>
     #include <linux/slab.h>
    #include <linux/file.h>
    #include <linux/fdtable.h>
    #include <linux/init.h>
    #include <linux/module.h>
    #include <linux/fs.h>
    #include <linux/security.h>
    #include <linux/eventpoll.h>
    #include <linux/rcupdate.h>
    #include <linux/mount.h>
    #include <linux/capability.h>
    #include <linux/cdev.h>
    #include <linux/fsnotify.h>
    #include <linux/sysctl.h>
    #include <linux/lglock.h>
    #include <linux/percpu_counter.h>
    #include <linux/percpu.h>
    #include <linux/hardirq.h>
    #include <linux/task_work.h>
    #include <linux/ima.h>
    
    #include <linux/atomic.h>
    
    #include "internal.h"
    
    /* sysctl tunables... */
    struct files_stat_struct files_stat = {
            .max_files = NR_FILE
    };
    
    DEFINE_STATIC_LGLOCK(files_lglock);
    
    /* SLAB cache for file structures */
    static struct kmem_cache *filp_cachep __read_mostly;
    
    static struct percpu_counter nr_files __cacheline_aligned_in_smp;
    
    static void file_free_rcu(struct rcu_head *head)
    {
            struct file *f = container_of(head, struct file, f_u.fu_rcuhead);
    
            put_cred(f->f_cred);
            kmem_cache_free(filp_cachep, f);
    }
    
    static inline void file_free(struct file *f)
    {
            percpu_counter_dec(&nr_files);
            file_check_state(f);
            call_rcu(&f->f_u.fu_rcuhead, file_free_rcu);
    }
    
    /*
     * Return the total number of open files in the system
     */
    static long get_nr_files(void)
    {
            return percpu_counter_read_positive(&nr_files);
    }
    
    /*
     * Return the maximum number of open files in the system
     */
    unsigned long get_max_files(void)
    {
            return files_stat.max_files;
    }
    EXPORT_SYMBOL_GPL(get_max_files);
    
    /*
     * Handle nr_files sysctl
     */
    #if defined(CONFIG_SYSCTL) && defined(CONFIG_PROC_FS)
    int proc_nr_files(ctl_table *table, int write,
                         void __user *buffer, size_t *lenp, loff_t *ppos)
    {
            files_stat.nr_files = get_nr_files();
            return proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
    }
    #else
    int proc_nr_files(ctl_table *table, int write,
                         void __user *buffer, size_t *lenp, loff_t *ppos)
    {
            return -ENOSYS;
    }
    #endif
    
    /* Find an unused file structure and return a pointer to it.
     * Returns NULL, if there are no more free file structures or
     * we run out of memory.
     *
    * Be very careful using this.  You are responsible for
    * getting write access to any mount that you might assign
    * to this filp, if it is opened for write.  If this is not
    * done, you will imbalance int the mount's writer count
    * and a warning at __fput() time.
    */
   struct file *get_empty_filp(void)
   {
           const struct cred *cred = current_cred();
           static long old_max;
           struct file * f;
   
           /*
            * Privileged users can go above max_files
            */
           if (get_nr_files() >= files_stat.max_files && !capable(CAP_SYS_ADMIN)) {
                   /*
                    * percpu_counters are inaccurate.  Do an expensive check before
                    * we go and fail.
                    */
                   if (percpu_counter_sum_positive(&nr_files) >= files_stat.max_files)
                           goto over;
           }
   
           f = kmem_cache_zalloc(filp_cachep, GFP_KERNEL);
           if (f == NULL)
                   goto fail;
   
           percpu_counter_inc(&nr_files);
           f->f_cred = get_cred(cred);
           if (security_file_alloc(f))
                   goto fail_sec;
   
           INIT_LIST_HEAD(&f->f_u.fu_list);
           atomic_long_set(&f->f_count, 1);
           rwlock_init(&f->f_owner.lock);
           spin_lock_init(&f->f_lock);
           eventpoll_init_file(f);
           /* f->f_version: 0 */
           return f;
   
   over:
           /* Ran out of filps - report that */
           if (get_nr_files() > old_max) {
                   pr_info("VFS: file-max limit %lu reached\n", get_max_files());
                   old_max = get_nr_files();
           }
           goto fail;
   
   fail_sec:
           file_free(f);
   fail:
           return NULL;
   }
   
   /**
    * alloc_file - allocate and initialize a 'struct file'
    * @mnt: the vfsmount on which the file will reside
    * @dentry: the dentry representing the new file
    * @mode: the mode with which the new file will be opened
    * @fop: the 'struct file_operations' for the new file
    *
    * Use this instead of get_empty_filp() to get a new
    * 'struct file'.  Do so because of the same initialization
    * pitfalls reasons listed for init_file().  This is a
    * preferred interface to using init_file().
    *
    * If all the callers of init_file() are eliminated, its
    * code should be moved into this function.
    */
   struct file *alloc_file(struct path *path, fmode_t mode,
                   const struct file_operations *fop)
   {
           struct file *file;
   
           file = get_empty_filp();
           if (!file)
                   return NULL;
   
           file->f_path = *path;
           file->f_mapping = path->dentry->d_inode->i_mapping;
           file->f_mode = mode;
           file->f_op = fop;
   
           /*
            * These mounts don't really matter in practice
            * for r/o bind mounts.  They aren't userspace-
            * visible.  We do this for consistency, and so
            * that we can do debugging checks at __fput()
            */
           if ((mode & FMODE_WRITE) && !special_file(path->dentry->d_inode->i_mode)) {
                   file_take_write(file);
                   WARN_ON(mnt_clone_write(path->mnt));
           }
           if ((mode & (FMODE_READ | FMODE_WRITE)) == FMODE_READ)
                   i_readcount_inc(path->dentry->d_inode);
           return file;
   }
   EXPORT_SYMBOL(alloc_file);
   
   /**
    * drop_file_write_access - give up ability to write to a file
    * @file: the file to which we will stop writing
    *
    * This is a central place which will give up the ability
    * to write to @file, along with access to write through
    * its vfsmount.
    */
   static void drop_file_write_access(struct file *file)
   {
           struct vfsmount *mnt = file->f_path.mnt;
           struct dentry *dentry = file->f_path.dentry;
           struct inode *inode = dentry->d_inode;
   
           put_write_access(inode);
   
           if (special_file(inode->i_mode))
                   return;
           if (file_check_writeable(file) != 0)
                   return;
           __mnt_drop_write(mnt);
           file_release_write(file);
   }
   
   /* the real guts of fput() - releasing the last reference to file
    */
   static void __fput(struct file *file)
   {
           struct dentry *dentry = file->f_path.dentry;
           struct vfsmount *mnt = file->f_path.mnt;
           struct inode *inode = dentry->d_inode;
   
           might_sleep();
   
           fsnotify_close(file);
           /*
            * The function eventpoll_release() should be the first called
            * in the file cleanup chain.
            */
           eventpoll_release(file);
           locks_remove_flock(file);
   
           if (unlikely(file->f_flags & FASYNC)) {
                   if (file->f_op && file->f_op->fasync)
                           file->f_op->fasync(-1, file, 0);
           }
           ima_file_free(file);
           if (file->f_op && file->f_op->release)
                   file->f_op->release(inode, file);
           security_file_free(file);
           if (unlikely(S_ISCHR(inode->i_mode) && inode->i_cdev != NULL &&
                        !(file->f_mode & FMODE_PATH))) {
                   cdev_put(inode->i_cdev);
           }
           fops_put(file->f_op);
           put_pid(file->f_owner.pid);
           if ((file->f_mode & (FMODE_READ | FMODE_WRITE)) == FMODE_READ)
                   i_readcount_dec(inode);
           if (file->f_mode & FMODE_WRITE)
                   drop_file_write_access(file);
           file->f_path.dentry = NULL;
           file->f_path.mnt = NULL;
           file_free(file);
           dput(dentry);
           mntput(mnt);
   }
   
   static DEFINE_SPINLOCK(delayed_fput_lock);
   static LIST_HEAD(delayed_fput_list);
   static void delayed_fput(struct work_struct *unused)
   {
           LIST_HEAD(head);
           spin_lock_irq(&delayed_fput_lock);
           list_splice_init(&delayed_fput_list, &head);
           spin_unlock_irq(&delayed_fput_lock);
           while (!list_empty(&head)) {
                   struct file *f = list_first_entry(&head, struct file, f_u.fu_list);
                   list_del_init(&f->f_u.fu_list);
                   __fput(f);
           }
   }
   
   static void ____fput(struct callback_head *work)
   {
           __fput(container_of(work, struct file, f_u.fu_rcuhead));
   }
   
   /*
    * If kernel thread really needs to have the final fput() it has done
    * to complete, call this.  The only user right now is the boot - we
    * *do* need to make sure our writes to binaries on initramfs has
    * not left us with opened struct file waiting for __fput() - execve()
    * won't work without that.  Please, don't add more callers without
    * very good reasons; in particular, never call that with locks
    * held and never call that from a thread that might need to do
    * some work on any kind of umount.
    */
   void flush_delayed_fput(void)
   {
           delayed_fput(NULL);
   }
   
   static DECLARE_WORK(delayed_fput_work, delayed_fput);
   
   void fput(struct file *file)
   {
           if (atomic_long_dec_and_test(&file->f_count)) {
                   struct task_struct *task = current;
                   file_sb_list_del(file);
                   if (unlikely(in_interrupt() || task->flags & PF_KTHREAD)) {
                           unsigned long flags;
                           spin_lock_irqsave(&delayed_fput_lock, flags);
                           list_add(&file->f_u.fu_list, &delayed_fput_list);
                           schedule_work(&delayed_fput_work);
                           spin_unlock_irqrestore(&delayed_fput_lock, flags);
                           return;
                   }
                   init_task_work(&file->f_u.fu_rcuhead, ____fput);
                   task_work_add(task, &file->f_u.fu_rcuhead, true);
           }
   }
   
   /*
    * synchronous analog of fput(); for kernel threads that might be needed
    * in some umount() (and thus can't use flush_delayed_fput() without
    * risking deadlocks), need to wait for completion of __fput() and know
    * for this specific struct file it won't involve anything that would
    * need them.  Use only if you really need it - at the very least,
    * don't blindly convert fput() by kernel thread to that.
    */
   void __fput_sync(struct file *file)
   {
           if (atomic_long_dec_and_test(&file->f_count)) {
                   struct task_struct *task = current;
                   file_sb_list_del(file);
                   BUG_ON(!(task->flags & PF_KTHREAD));
                   __fput(file);
           }
   }
   
   EXPORT_SYMBOL(fput);
   
   void put_filp(struct file *file)
   {
           if (atomic_long_dec_and_test(&file->f_count)) {
                   security_file_free(file);
                   file_sb_list_del(file);
                   file_free(file);
           }
   }
   
   static inline int file_list_cpu(struct file *file)
   {
   #ifdef CONFIG_SMP
           return file->f_sb_list_cpu;
   #else
           return smp_processor_id();
   #endif
   }
   
   /* helper for file_sb_list_add to reduce ifdefs */
   static inline void __file_sb_list_add(struct file *file, struct super_block *sb)
   {
           struct list_head *list;
   #ifdef CONFIG_SMP
           int cpu;
           cpu = smp_processor_id();
           file->f_sb_list_cpu = cpu;
           list = per_cpu_ptr(sb->s_files, cpu);
   #else
           list = &sb->s_files;
   #endif
           list_add(&file->f_u.fu_list, list);
   }
   
   /**
    * file_sb_list_add - add a file to the sb's file list
    * @file: file to add
    * @sb: sb to add it to
    *
    * Use this function to associate a file with the superblock of the inode it
    * refers to.
    */
   void file_sb_list_add(struct file *file, struct super_block *sb)
   {
           lg_local_lock(&files_lglock);
           __file_sb_list_add(file, sb);
           lg_local_unlock(&files_lglock);
   }
   
   /**
    * file_sb_list_del - remove a file from the sb's file list
    * @file: file to remove
    * @sb: sb to remove it from
    *
    * Use this function to remove a file from its superblock.
    */
   void file_sb_list_del(struct file *file)
   {
           if (!list_empty(&file->f_u.fu_list)) {
                   lg_local_lock_cpu(&files_lglock, file_list_cpu(file));
                   list_del_init(&file->f_u.fu_list);
                   lg_local_unlock_cpu(&files_lglock, file_list_cpu(file));
           }
   }
   
   #ifdef CONFIG_SMP
   
   /*
    * These macros iterate all files on all CPUs for a given superblock.
    * files_lglock must be held globally.
    */
   #define do_file_list_for_each_entry(__sb, __file)               \
   {                                                               \
           int i;                                                  \
           for_each_possible_cpu(i) {                              \
                   struct list_head *list;                         \
                   list = per_cpu_ptr((__sb)->s_files, i);         \
                   list_for_each_entry((__file), list, f_u.fu_list)
   
   #define while_file_list_for_each_entry                          \
           }                                                       \
   }
   
   #else
   
   #define do_file_list_for_each_entry(__sb, __file)               \
   {                                                               \
           struct list_head *list;                                 \
           list = &(sb)->s_files;                                  \
           list_for_each_entry((__file), list, f_u.fu_list)
   
   #define while_file_list_for_each_entry                          \
   }
   
   #endif
   
   /**
    *      mark_files_ro - mark all files read-only
    *      @sb: superblock in question
    *
    *      All files are marked read-only.  We don't care about pending
    *      delete files so this should be used in 'force' mode only.
    */
   void mark_files_ro(struct super_block *sb)
   {
           struct file *f;
   
           lg_global_lock(&files_lglock);
           do_file_list_for_each_entry(sb, f) {
                   if (!S_ISREG(f->f_path.dentry->d_inode->i_mode))
                          continue;
                   if (!file_count(f))
                           continue;
                   if (!(f->f_mode & FMODE_WRITE))
                           continue;
                   spin_lock(&f->f_lock);
                   f->f_mode &= ~FMODE_WRITE;
                   spin_unlock(&f->f_lock);
                   if (file_check_writeable(f) != 0)
                           continue;
                   __mnt_drop_write(f->f_path.mnt);
                   file_release_write(f);
           } while_file_list_for_each_entry;
           lg_global_unlock(&files_lglock);
   }
   
   void __init files_init(unsigned long mempages)
   { 
           unsigned long n;
   
           filp_cachep = kmem_cache_create("filp", sizeof(struct file), 0,
                           SLAB_HWCACHE_ALIGN | SLAB_PANIC, NULL);
   
           /*
            * One file with associated inode and dcache is very roughly 1K.
            * Per default don't use more than 10% of our memory for files. 
            */ 
   
           n = (mempages * (PAGE_SIZE / 1024)) / 10;
           files_stat.max_files = max_t(unsigned long, n, NR_FILE);
           files_defer_init();
           lg_lock_init(&files_lglock, "files_lglock");
           percpu_counter_init(&nr_files, 0);
   } 

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