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 82d3f925bab391c43832baf6ccf8e164ae318964..a42683abb323acb9647c0cb938f2e03c72b188ac 100644 (file)
--- a/fs/file.c
+++ b/fs/file.c
@@ -692,7 +692,7 @@ 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;
@@ -707,7 +707,7 @@ static struct file *__fget(unsigned int fd, fmode_t mask)
                 */
                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();
@@ -715,15 +715,20 @@ static struct file *__fget(unsigned int fd, fmode_t mask)
        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);
 
@@ -754,7 +759,7 @@ 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 ad17e05ebf95f07888b15f2b09a7b37ac89b9710..747bb386b44661fd1945c20ec45814811b1a2c6a 100644 (file)
--- a/fs/file_table.c
+++ b/fs/file_table.c
@@ -261,9 +261,9 @@ 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))) {
@@ -282,6 +282,11 @@ 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 7444f5feda12559b5bf5fd5dd564226da1157eeb..d5baf7194fb0b5d312bb07b521990951f49ca257 100644 (file)
--- a/include/linux/file.h
+++ b/include/linux/file.h
@@ -12,6 +12,7 @@
 struct file;
 
 extern void fput(struct file *);
+extern void fput_many(struct file *, unsigned int);
 
 struct file_operations;
 struct vfsmount;
@@ -40,6 +41,7 @@ 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 b8d65e0ab934124f9c5e7ba074e985061dc47a58..9e4a75005280f533946f3cca44c52888303e18b8 100644 (file)
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -939,7 +939,9 @@ 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)