[PATCH] files: break up files struct

In order for the RCU to work, the file table array, sets and their sizes must
be updated atomically.  Instead of ensuring this through too many memory
barriers, we put the arrays and their sizes in a separate structure.  This
patch takes the first step of putting the file table elements in a separate
structure fdtable that is embedded withing files_struct.  It also changes all
the users to refer to the file table using files_fdtable() macro.  Subsequent
applciation of RCU becomes easier after this.

Signed-off-by: Dipankar Sarma <dipankar@in.ibm.com>
Signed-Off-By: David Howells <dhowells@redhat.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 29 insertions, 18 deletions

diff --git a/fs/fcntl.c b/fs/fcntl.c
index 6fbc9d8fcc36..bfecc6238083 100644
--- a/fs/fcntl.c
+++ b/fs/fcntl.c
@@ -24,20 +24,24 @@
 void fastcall set_close_on_exec(unsigned int fd, int flag)
 {
         struct files_struct *files = current->files;
+        struct fdtable *fdt;
         spin_lock(&files->file_lock);
+        fdt = files_fdtable(files);
         if (flag)
-                FD_SET(fd, files->close_on_exec);
+                FD_SET(fd, fdt->close_on_exec);
         else
-                FD_CLR(fd, files->close_on_exec);
+                FD_CLR(fd, fdt->close_on_exec);
         spin_unlock(&files->file_lock);
 }
 
 static inline int get_close_on_exec(unsigned int fd)
 {
         struct files_struct *files = current->files;
+        struct fdtable *fdt;
         int res;
         spin_lock(&files->file_lock);
-        res = FD_ISSET(fd, files->close_on_exec);
+        fdt = files_fdtable(files);
+        res = FD_ISSET(fd, fdt->close_on_exec);
         spin_unlock(&files->file_lock);
         return res;
 }
@@ -54,24 +58,26 @@ static int locate_fd(struct files_struct *files,
         unsigned int newfd;
         unsigned int start;
         int error;
+        struct fdtable *fdt;
 
         error = -EINVAL;
         if (orig_start >= current->signal->rlim[RLIMIT_NOFILE].rlim_cur)
                 goto out;
 
+        fdt = files_fdtable(files);
 repeat:
         /*
          * Someone might have closed fd's in the range
-         * orig_start..files->next_fd
+         * orig_start..fdt->next_fd
          */
         start = orig_start;
-        if (start < files->next_fd)
-                start = files->next_fd;
+        if (start < fdt->next_fd)
+                start = fdt->next_fd;
 
         newfd = start;
-        if (start < files->max_fdset) {
-                newfd = find_next_zero_bit(files->open_fds->fds_bits,
-                        files->max_fdset, start);
+        if (start < fdt->max_fdset) {
+                newfd = find_next_zero_bit(fdt->open_fds->fds_bits,
+                        fdt->max_fdset, start);
         }
         
         error = -EMFILE;
@@ -89,8 +95,8 @@ repeat:
         if (error)
                 goto repeat;
 
-        if (start <= files->next_fd)
-                files->next_fd = newfd + 1;
+        if (start <= fdt->next_fd)
+                fdt->next_fd = newfd + 1;
         
         error = newfd;
         
@@ -101,13 +107,16 @@ out:
 static int dupfd(struct file *file, unsigned int start)
 {
         struct files_struct * files = current->files;
+        struct fdtable *fdt;
         int fd;
 
         spin_lock(&files->file_lock);
         fd = locate_fd(files, file, start);
         if (fd >= 0) {
-                FD_SET(fd, files->open_fds);
-                FD_CLR(fd, files->close_on_exec);
+                /* locate_fd() may have expanded fdtable, load the ptr */
+                fdt = files_fdtable(files);
+                FD_SET(fd, fdt->open_fds);
+                FD_CLR(fd, fdt->close_on_exec);
                 spin_unlock(&files->file_lock);
                 fd_install(fd, file);
         } else {
@@ -123,6 +132,7 @@ asmlinkage long sys_dup2(unsigned int oldfd, unsigned int newfd)
         int err = -EBADF;
         struct file * file, *tofree;
         struct files_struct * files = current->files;
+        struct fdtable *fdt;
 
         spin_lock(&files->file_lock);
         if (!(file = fcheck(oldfd)))
@@ -148,13 +158,14 @@ asmlinkage long sys_dup2(unsigned int oldfd, unsigned int newfd)
 
         /* Yes. It's a race. In user space. Nothing sane to do */
         err = -EBUSY;
-        tofree = files->fd[newfd];
-        if (!tofree && FD_ISSET(newfd, files->open_fds))
+        fdt = files_fdtable(files);
+        tofree = fdt->fd[newfd];
+        if (!tofree && FD_ISSET(newfd, fdt->open_fds))
                 goto out_fput;
 
-        files->fd[newfd] = file;
-        FD_SET(newfd, files->open_fds);
-        FD_CLR(newfd, files->close_on_exec);
+        fdt->fd[newfd] = file;
+        FD_SET(newfd, fdt->open_fds);
+        FD_CLR(newfd, fdt->close_on_exec);
         spin_unlock(&files->file_lock);
 
         if (tofree)