hci connect and switch role modifications

Hi Marcel,

in february I sent you the email in the following, about some proposed modifications in the HCI connect and switch role APIs. At that time, I also attached you the unified diff files, which I'm attaching also now. Anyway, I didn't receive any reply. Do you think these modifications are likely to be integrated in next releases?
Thanks,
Marcello.

Subject:
Re: [Bluez-devel] hci connect and switch role modifications From:
Capaianca <[email protected]>
Date:
Tue, 21 Feb 2006 17:03:36 +0100

To:
[email protected]

Hi Marcel,

as requested, we have attached the unified diff files of our
modifications. Basically, we added a couple mechanisms that may use to prevent some errors from occurring (error masking mechanisms). The mechanisms are part of the results of our research on bluetooth networks. Perhaps the same strategies can be generalized and applied on several parts of the code in order to improve the overall robustness of the BlueZ stack.

Specifically, in the hci.c file (and related hci_lib.h) we added two functions that may help to solve some problems which may arise when creating connections or when switching the role. These functions are called "hci_create_connection_timed" and "hci_switch_role_checked".

The hci_create_connection_timed function first creates a connection and then checks whether the handle is valid (>0) until a given timeout expires. The timeout is specified as an additional parameter, in milliseconds.
We created this function because, while working with bluetooth, we noticed that to get a valid handle over a connection may take some time, even after that the hci_create_connection function return, due to the asynchronous nature of the connection creation process. This could result in a error when subsequent calls are performed over the connection with a handle that is still not valid (e.g. a bnep create connection call over an already created l2cap connection, or a switch role command). This function avoids this problem because it returns with no errors only if the created connection has a valid handle. It is worth noting that the function returns a "timer expired (ETIME)" error even when the connection is created. This happens when the timeout expires but the connection still has a not valid handle. However, the handle could become valid after the function exits.

The hci_switch_role_checked function performs a similar task. During our tests we noticed that sometimes the hci_switch_role function exits with a EIO error even if the role was actually switched. This problem may be due to a temporary bad state of the rp.status value during the switch role process attempt. To overcome this problem, after an invalid check of rp.status value, our function reads the linkmode of the connection to check the real status after a little amount of time (100ms in the current version). If the role is not switched, further attempts are made until a timeout expires. This timeout is provided as an input parameter to our function. This function resulted particularly useful when using PDA and other limited resources devices where the time required to perform the switch role may be longer and may result in errors signaled by the original hci_switch_role function even if the role was actually switched.

We preferred to provide two new functions rather than modifying the original ones. This way the user can choose to use the function that better suites his requirements.

In order to test and use the new functionalities, we also slightly modified the hcitool.c program, so as to add an optional parameter "--timeout" to both the "cc" and "sr" commands. If the parameter is specified the new functions are called, otherwise the original functions are used.

Hope this can be of interest and help the BlueZ community.

Best regards,
Marcello Cinque
Fabio Cornevilli
Mobilab Research Group - www.mobilab.unina.it

Hi Marcello,

simply sent a unified diff against the latest CVS to the mailing list.

Regards

Marcel

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Hi Marcello,

I might have missed that. Sorry, but this can happen from time to time.

If you propose multiple changes then please split them and post them separately if possible. This makes it easier for me to review them and then integrate them.

Regards

Marcel

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Hi Marcel,

as you asked, i'll send you the modifications separately.

This is the first.
Basically, we added a mechanism that may use to prevent some errors from occurring (error masking mechanism) when performing a hci_create_connection. The mechanism is part of the results of our research on bluetooth networks. Perhaps the same strategies can be generalized and applied on several parts of the code in order to improve the overall robustness of the BlueZ stack.
Specifically we added a function to the hci.c file (and related hci_lib.h) which name is hci_create_connection_timed.
This function first creates a connection and then checks whether the handle is valid (>0) until a given timeout expires. The timeout is specified as an additional parameter, in milliseconds. We created this function because, while working with bluetooth, we noticed that to get a valid handle over a connection may take some time, even after that the hci_create_connection function return, due to the asynchronous nature of the connection creation process. This could result in a error when subsequent calls are performed over the connection with a handle that is still not valid (e.g. a bnep create connection call over an already created l2cap connection, or a switch role command). This function avoids this problem because it returns with no errors only if the created connection has a valid handle. It is worth noting that the function returns a "timer expired (ETIME)" error even when the connection is created. This happens when the timeout expires but the connection still has a not valid handle. However, the handle could become valid after the function exits.

We preferred to provide a new function rather than modifying the original ones. This way the user can choose to use the function that better suites his requirements.

In order to test and use the new functionalities, we also slightly modified the hcitool.c program, so as to add an optional parameter "--timeout" to the "cc" command. If the parameter is specified the new functions are called, otherwise the original functions are used.

Let me know if this can be of interest, in which case I'll send you also the second modification, on the switch role command.

Best regards,
Marcello Cinque
Fabio Cornevilli
Mobilab Research Group - www.mobilab.unina.it

Marcello Cinque, PhD Candidate
Dipartimento di Informatica e Sistemistica
Università di Napoli Federico II
Via Claudio, 21 - 80125 Napoli, Italy
Ph:  +39-081-7683874
Fax: +39-081-7683816
Web: wpage.unina.it/macinque
The MobiLab Group - www.mobilab.unina.it 


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