Re: [RFC 1/1] update index for serial device using taget.port

On 24/11/21 6:21 pm, Peter Krempa wrote: This patch was just for getting the understanding of historical reasons of the port allocation logic we process today and if the changes suggested looks good and doesn't violate any convention or if we are planning to have a different handling for such cases. I am really sorry for that, I didnt give much attention to that. It was just to show how I will be changing the port allocation logic for isa-serial devices. Noted. Thanks. Noted Noted Earlier we never checked for repeated ports or the max port that can be assigned to a particular design. Besides we used to assign the ports blindly without considering what kind of device it is. Was there any specefic reason for this ? Thanks, but this will be anyhow required to check if the device is ISA-serial or not. Will update the allignment. Hi Peter. This was an RFC and yeah, still not finalised. I will be working on formatting and restructure the code once the logic goods. Before putting more efforts in finalising the code I wanted to confirm if the changes in the port allocation logic for isa-serial devices looks good or not. Sharing the details : _*Issue*_ ----- The port being provided in the xml file of the domain is not being used for the creation of qemu command. On adding the serial device : <serial<target type='serial' port='3'/</serial Generated qemu command will look like : /usr/libexec/qemu-kvm ...\     -device isa-serial,chardev=charserial0,id=serial0 Actually it should be : /usr/libexec/qemu-kvm ...\     -device isa-serial,chardev=charserial0,id=serial0,index=3 There is a patch out there already for the correction : https://listman.redhat.com/archives/libvir-list/2018-April/msg02302.html But This patch was not followed up. According to me there are multiple reasons _*Reasons for not following up*_ ---------------------------- ---------------------------- Index : specifies the index number of a connector port. If not specified, the index is automatically incremented. This logic exists both on qemu as well as libvirt. https://github.com/qemu/qemu/blob/master/hw/char/serial-isa.c#L62 _*Issue 1:*_ If we want two isa-serial devices and for the first one is we mention the port to be 3, then for the next device it not automatically assign the port number 4 which will throw the following error : error: internal error: process exited while connecting to monitor: 2021-11-12T11:05:31.169987Z qemu-kvm: -device isa-serial,chardev=charserial2,id=serial2,index=5: Max. supported number of ISA serial ports is 4. But we are left with 3 ports (0,1,2) which are unused. So ideally we should have used them. _*Issue 2:*_** It is possible that two devices get the same port address which might lead to a lot of ambiguity. Example: we want two devices and for the second one we provide the index 0. Then from default logic the first device will be allotted port 0 and the second device will overwrite it and get port 0. _*Solution :*_ ---------- ---------- *_Port allocation logic_* 1. Precedence should be given to serial devices as we only have the first 4 ports for them.     1.1. Check the command line/xml file, scan for all the devices mentioned     and then start with the isa-serial devices for port allocation. 2.Maintain a buffer(bitmap) for marking the allocated ports. 3.While assigning a port to the device     3.1. If no port is provided by the user : provide the next available port.     3.2. Else check:         3.2.1. If the port is already allocated : throw the error.         3.2.2. Else allocate the port.     3.3. If out of ports : throw error -> qemu throws the error. Libvirt also manages the port numbers with the auto increment logic but never updates the index value using the port number. Hence index should be assigned with proper port allocation logic.