Re: [PATCH v3] usb: gadget: f_fs: add "no_disconnect" mode
From: Robert Baldyga
Date: Fri Oct 10 2014 - 04:10:42 EST
On 10/09/2014 03:57 PM, Michal Nazarewicz wrote:
> On Thu, Oct 09 2014, Robert Baldyga <r.baldyga@xxxxxxxxxxx> 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>
>
> Acked-by: Michal Nazarewicz <mina86@xxxxxxxxxx>
>
> Even though I have some concerns whether the mode should be enable via
> a mount option. Perhaps it should come from the gadget or the daemon?
> I don't have strong feelings though, so I would be fine with the code as
> is.
>
I think that setting this option by daemon isn't good idea. It's better
to have this feature transparent for ffs daemons, and allow user to
decide how the function should behave after daemon breakage/termination.
This feature makes sense only because we don't want to have entire
gadget work dependent on ffs daemon, which is userspace code and we have
no guarantee it works properly.
Thanks,
Robert Baldyga
>> ---
>>
>> Changelog:
>>
>> v3:
>> - 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..f326267 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_clear(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
>>
>
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