Re: [PATCH v4] usb: gadget: f_fs: add "no_disconnect" mode

From: Felipe Balbi
Date: Mon Nov 03 2014 - 11:11:43 EST


Hi,

On Thu, Oct 09, 2014 at 03:21:51PM +0200, Robert Baldyga wrote:
> Since we can compose gadgets from many functions, there is the problem
> related to gadget breakage while FunctionFS daemon being closed. FFS
> function is userspace code so there is no way to know when it will close
> files (it doesn't matter what is the reason of this situation, it can
> be daemon logic, program breakage, process kill or any other). So when
> we have another function in gadget which, for example, sends some amount
> of data, does some software update or implements some real-time functionality,
> we may want to keep the gadget connected despite FFS function is no longer
> functional.
>
> We can't just remove one of functions from gadget since it has been
> enumerated, so the only way to keep entire gadget working is to make
> broken FFS function deactivated but still visible to host. For this
> purpose this patch introduces "no_disconnect" mode. It can be enabled
> by setting mount option "no_disconnect=1", and results with defering
> function disconnect to the moment of reopen ep0 file or filesystem
> unmount. After closing all endpoint files, FunctionFS is set to state
> FFS_DEACTIVATED.
>
> When ffs->state == FFS_DEACTIVATED:
> - function is still bound and visible to host,
> - setup requests are automatically stalled,
> - transfers on other endpoints are refused,
> - epfiles, except ep0, are deleted from the filesystem,
> - opening ep0 causes the function to be closes, and then FunctionFS
> is ready for descriptors and string write,
> - unmounting of the FunctionFS instance causes the function to be closed.
>
> Signed-off-by: Robert Baldyga <r.baldyga@xxxxxxxxxxx>

David, you have been messing with ffs lately, can I get a Tested-by from
you on this patch ?

> ---
>
> Changelog:
>
> v4:
> - use ffs_data_reset() instead of ffs_data_clear() to reset ffs data
> properly after ffs->ref refcount reach 0 (or under in no_disconnect
> mode) in ffs_data_put() function
>
> v3: https://lkml.org/lkml/2014/10/9/170
> - change option name to more descriptive and less scary,
> - fix cleaning up on unmount (call ffs_data_closed() in ffs_fs_kill_sb(),
> and ffs_data_clear() in ffs_data_closed() if ffs->opened is negative).
>
> v2: https://lkml.org/lkml/2014/10/7/109
> - delete epfiles, excepting ep0, when FFS is in "zombie" mode,
> - add description of FFS_ZOMBIE state,
> - minor cleanups.
>
> v1: https://lkml.org/lkml/2014/10/6/128
>
> drivers/usb/gadget/function/f_fs.c | 42 +++++++++++++++++++++++++++++++-------
> drivers/usb/gadget/function/u_fs.h | 22 ++++++++++++++++++++
> 2 files changed, 57 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/usb/gadget/function/f_fs.c b/drivers/usb/gadget/function/f_fs.c
> index 12dbdaf..2d47d4a 100644
> --- a/drivers/usb/gadget/function/f_fs.c
> +++ b/drivers/usb/gadget/function/f_fs.c
> @@ -606,6 +606,8 @@ static unsigned int ffs_ep0_poll(struct file *file, poll_table *wait)
> }
> case FFS_CLOSING:
> break;
> + case FFS_DEACTIVATED:
> + break;
> }
>
> mutex_unlock(&ffs->mutex);
> @@ -1152,6 +1154,7 @@ struct ffs_sb_fill_data {
> struct ffs_file_perms perms;
> umode_t root_mode;
> const char *dev_name;
> + bool no_disconnect;
> struct ffs_data *ffs_data;
> };
>
> @@ -1222,6 +1225,12 @@ static int ffs_fs_parse_opts(struct ffs_sb_fill_data *data, char *opts)
>
> /* Interpret option */
> switch (eq - opts) {
> + case 13:
> + if (!memcmp(opts, "no_disconnect", 13))
> + data->no_disconnect = !!value;
> + else
> + goto invalid;
> + break;
> case 5:
> if (!memcmp(opts, "rmode", 5))
> data->root_mode = (value & 0555) | S_IFDIR;
> @@ -1286,6 +1295,7 @@ ffs_fs_mount(struct file_system_type *t, int flags,
> .gid = GLOBAL_ROOT_GID,
> },
> .root_mode = S_IFDIR | 0500,
> + .no_disconnect = false,
> };
> struct dentry *rv;
> int ret;
> @@ -1302,6 +1312,7 @@ ffs_fs_mount(struct file_system_type *t, int flags,
> if (unlikely(!ffs))
> return ERR_PTR(-ENOMEM);
> ffs->file_perms = data.perms;
> + ffs->no_disconnect = data.no_disconnect;
>
> ffs->dev_name = kstrdup(dev_name, GFP_KERNEL);
> if (unlikely(!ffs->dev_name)) {
> @@ -1333,6 +1344,7 @@ ffs_fs_kill_sb(struct super_block *sb)
> kill_litter_super(sb);
> if (sb->s_fs_info) {
> ffs_release_dev(sb->s_fs_info);
> + ffs_data_closed(sb->s_fs_info);
> ffs_data_put(sb->s_fs_info);
> }
> }
> @@ -1389,7 +1401,9 @@ static void ffs_data_opened(struct ffs_data *ffs)
> ENTER();
>
> atomic_inc(&ffs->ref);
> - atomic_inc(&ffs->opened);
> + if (atomic_add_return(1, &ffs->opened) == 1)
> + if (ffs->state == FFS_DEACTIVATED)
> + ffs_data_reset(ffs);
> }
>
> static void ffs_data_put(struct ffs_data *ffs)
> @@ -1411,9 +1425,22 @@ static void ffs_data_closed(struct ffs_data *ffs)
> ENTER();
>
> if (atomic_dec_and_test(&ffs->opened)) {
> - ffs->state = FFS_CLOSING;
> - ffs_data_reset(ffs);
> + if (ffs->no_disconnect) {
> + ffs->state = FFS_DEACTIVATED;
> + if (ffs->epfiles) {
> + ffs_epfiles_destroy(ffs->epfiles,
> + ffs->eps_count);
> + ffs->epfiles = NULL;
> + }
> + if (ffs->setup_state == FFS_SETUP_PENDING)
> + __ffs_ep0_stall(ffs);
> + } else {
> + ffs->state = FFS_CLOSING;
> + ffs_data_reset(ffs);
> + }
> }
> + if (atomic_read(&ffs->opened) < 0)
> + ffs_data_reset(ffs);
>
> ffs_data_put(ffs);
> }
> @@ -1588,7 +1615,6 @@ static void ffs_epfiles_destroy(struct ffs_epfile *epfiles, unsigned count)
> kfree(epfiles);
> }
>
> -
> static void ffs_func_eps_disable(struct ffs_function *func)
> {
> struct ffs_ep *ep = func->eps;
> @@ -1601,10 +1627,12 @@ static void ffs_func_eps_disable(struct ffs_function *func)
> /* pending requests get nuked */
> if (likely(ep->ep))
> usb_ep_disable(ep->ep);
> - epfile->ep = NULL;
> -
> ++ep;
> - ++epfile;
> +
> + if (epfile) {
> + epfile->ep = NULL;
> + ++epfile;
> + }
> } while (--count);
> spin_unlock_irqrestore(&func->ffs->eps_lock, flags);
> }
> diff --git a/drivers/usb/gadget/function/u_fs.h b/drivers/usb/gadget/function/u_fs.h
> index cd128e3..7bc0ca2 100644
> --- a/drivers/usb/gadget/function/u_fs.h
> +++ b/drivers/usb/gadget/function/u_fs.h
> @@ -93,6 +93,26 @@ enum ffs_state {
> FFS_ACTIVE,
>
> /*
> + * Function is visible to host, but it's not functional. All
> + * setup requests are stalled and transfers on another endpoints
> + * are refused. All epfiles, except ep0, are deleted so there
> + * is no way to perform any operations on them.
> + *
> + * This state is set after closing all functionfs files, when
> + * mount parameter "no_disconnect=1" has been set. Function will
> + * remain in deactivated state until filesystem is umounted or
> + * ep0 is opened again. In the second case functionfs state will
> + * be reset, and it will be ready for descriptors and strings
> + * writing.
> + *
> + * This is useful only when functionfs is composed to gadget
> + * with another function which can perform some critical
> + * operations, and it's strongly desired to have this operations
> + * completed, even after functionfs files closure.
> + */
> + FFS_DEACTIVATED,
> +
> + /*
> * All endpoints have been closed. This state is also set if
> * we encounter an unrecoverable error. The only
> * unrecoverable error is situation when after reading strings
> @@ -251,6 +271,8 @@ struct ffs_data {
> kgid_t gid;
> } file_perms;
>
> + bool no_disconnect;
> +
> /*
> * The endpoint files, filled by ffs_epfiles_create(),
> * destroyed by ffs_epfiles_destroy().
> --
> 1.9.1
>

--
balbi

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