fs: add fget_many() and fput_many()

commit 091141a42e15fe47ada737f3996b317072afcefb upstream.

Some uses cases repeatedly get and put references to the same file, but
the only exposed interface is doing these one at the time. As each of
these entail an atomic inc or dec on a shared structure, that cost can
add up.

Add fget_many(), which works just like fget(), except it takes an
argument for how many references to get on the file. Ditto fput_many(),
which can drop an arbitrary number of references to a file.

Reviewed-by: Hannes Reinecke <hare@suse.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/fs/file.c b/fs/file.c
index 3762a3f136fda96e3137b3f740d4ca43e26f6d89..ec6738ed907d82058cbdbaf663ef8252add74eb7 100644 (file)
--- a/fs/file.c
+++ b/fs/file.c
@@ -677,7 +677,7 @@ void do_close_on_exec(struct files_struct *files)
        spin_unlock(&files->file_lock);
 }
 
-static struct file *__fget(unsigned int fd, fmode_t mask)
+static struct file *__fget(unsigned int fd, fmode_t mask, unsigned int refs)
 {
        struct files_struct *files = current->files;
        struct file *file;
@@ -692,7 +692,7 @@ loop:
                 */
                if (file->f_mode & mask)
                        file = NULL;
-               else if (!get_file_rcu(file))
+               else if (!get_file_rcu_many(file, refs))
                        goto loop;
        }
        rcu_read_unlock();
@@ -700,15 +700,20 @@ loop:
        return file;
 }
 
+struct file *fget_many(unsigned int fd, unsigned int refs)
+{
+       return __fget(fd, FMODE_PATH, refs);
+}
+
 struct file *fget(unsigned int fd)
 {
-       return __fget(fd, FMODE_PATH);
+       return __fget(fd, FMODE_PATH, 1);
 }
 EXPORT_SYMBOL(fget);
 
 struct file *fget_raw(unsigned int fd)
 {
-       return __fget(fd, 0);
+       return __fget(fd, 0, 1);
 }
 EXPORT_SYMBOL(fget_raw);
 
@@ -739,7 +744,7 @@ static unsigned long __fget_light(unsigned int fd, fmode_t mask)
                        return 0;
                return (unsigned long)file;
        } else {
-               file = __fget(fd, mask);
+               file = __fget(fd, mask, 1);
                if (!file)
                        return 0;
                return FDPUT_FPUT | (unsigned long)file;

diff --git a/fs/file_table.c b/fs/file_table.c
index e49af4caf15d92e3a33bbd02e4e551d778d8180e..6a715639728daa5143c8359ede72bb301d5ec40e 100644 (file)
--- a/fs/file_table.c
+++ b/fs/file_table.c
@@ -326,9 +326,9 @@ void flush_delayed_fput(void)
 
 static DECLARE_DELAYED_WORK(delayed_fput_work, delayed_fput);
 
-void fput(struct file *file)
+void fput_many(struct file *file, unsigned int refs)
 {
-       if (atomic_long_dec_and_test(&file->f_count)) {
+       if (atomic_long_sub_and_test(refs, &file->f_count)) {
                struct task_struct *task = current;
 
                if (likely(!in_interrupt() && !(task->flags & PF_KTHREAD))) {
@@ -347,6 +347,11 @@ void fput(struct file *file)
        }
 }
 
+void fput(struct file *file)
+{
+       fput_many(file, 1);
+}
+
 /*
  * synchronous analog of fput(); for kernel threads that might be needed
  * in some umount() (and thus can't use flush_delayed_fput() without

diff --git a/include/linux/file.h b/include/linux/file.h
index 6b2fb032416ca2fcf285c199aeb43aa845f3ac00..3fcddff56bc4bb30b7ac46da444be05a771964bf 100644 (file)
--- a/include/linux/file.h
+++ b/include/linux/file.h
@@ -13,6 +13,7 @@
 struct file;
 
 extern void fput(struct file *);
+extern void fput_many(struct file *, unsigned int);
 
 struct file_operations;
 struct vfsmount;
@@ -44,6 +45,7 @@ static inline void fdput(struct fd fd)
 }
 
 extern struct file *fget(unsigned int fd);
+extern struct file *fget_many(unsigned int fd, unsigned int refs);
 extern struct file *fget_raw(unsigned int fd);
 extern unsigned long __fdget(unsigned int fd);
 extern unsigned long __fdget_raw(unsigned int fd);

diff --git a/include/linux/fs.h b/include/linux/fs.h
index b6a955ba6173afde56e2a9adbb938e0307c65ffa..86f884e78b6b9f1441848218ac6186c45f98dbe2 100644 (file)
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -942,7 +942,9 @@ static inline struct file *get_file(struct file *f)
        atomic_long_inc(&f->f_count);
        return f;
 }
-#define get_file_rcu(x) atomic_long_inc_not_zero(&(x)->f_count)
+#define get_file_rcu_many(x, cnt)      \
+       atomic_long_add_unless(&(x)->f_count, (cnt), 0)
+#define get_file_rcu(x) get_file_rcu_many((x), 1)
 #define fput_atomic(x) atomic_long_add_unless(&(x)->f_count, -1, 1)
 #define file_count(x)  atomic_long_read(&(x)->f_count)