Re: [PATCH v2 1/2] fs: Improve and simplify copy_mount_options

Willy Tarreau
2016-06-16T08:38:08Z

On Thu, Jun 16, 2016 at 10:20:38AM +0200, Willy Tarreau wrote:
> However if the initial point was to avoid reading extra
> pages most of the time, we could possibly consider that the string
> copy is an optimization for the case where we have the information
> available. Thus if !fstype || !(type->fs_flags & FS_BINARY_MOUNTDATA)
> then we use copy_mount_options() otherwise we use copy_mount_string().
> It will only leave the full page copy for mount --bind or -o remount
> then.

For example like this (not compile-tested either) :

diff --git a/fs/compat.c b/fs/compat.c
index be6e48b..6407d40 100644
--- a/fs/compat.c
+++ b/fs/compat.c
@@ -795,18 +795,26 @@ COMPAT_SYSCALL_DEFINE5(mount, const char __user *, dev_name,
void *options;
char *kernel_dev;
int retval;
+ bool use_str = false;
+ struct file_system_type *fstype;

kernel_type = copy_mount_string(type);
retval = PTR_ERR(kernel_type);
if (IS_ERR(kernel_type))
goto out;

+ if (kernel_type && (fstype = get_fs_type(kernel_type)) {
+ if (!(fstype->fs_flags & FS_BINARY_MOUNTDATA))
+ use_str = true;
+ put_filesystem(fstype);
+ }
+
kernel_dev = copy_mount_string(dev_name);
retval = PTR_ERR(kernel_dev);
if (IS_ERR(kernel_dev))
goto out1;

- options = copy_mount_options(data);
+ options = use_str ? copy_mount_string(data) : copy_mount_options(data);
retval = PTR_ERR(options);
if (IS_ERR(options))
goto out2;
diff --git a/fs/namespace.c b/fs/namespace.c
index 4fb1691..f14089d 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -2906,18 +2906,26 @@ SYSCALL_DEFINE5(mount, char __user *, dev_name, char __user *, dir_name,
char *kernel_type;
char *kernel_dev;
void *options;
+ bool use_str = false;
+ struct file_system_type *fstype;

kernel_type = copy_mount_string(type);
ret = PTR_ERR(kernel_type);
if (IS_ERR(kernel_type))
goto out_type;

+ if (kernel_type && (fstype = get_fs_type(kernel_type)) {
+ if (!(fstype->fs_flags & FS_BINARY_MOUNTDATA))
+ use_str = true;
+ put_filesystem(fstype);
+ }
+
kernel_dev = copy_mount_string(dev_name);
ret = PTR_ERR(kernel_dev);
if (IS_ERR(kernel_dev))
goto out_dev;

- options = copy_mount_options(data);
+ options = use_str ? copy_mount_string(data) : copy_mount_options(data);
ret = PTR_ERR(options);
if (IS_ERR(options))
goto out_data;