Re: [Scst-devel] SCST User Space Registration Problems

[Vladislav B. <vs...@vl...>]

Hi,

There is a code example at 
https://github.com/SCST-project/scst/tree/master/usr/fileio, you can 
look how it works.

Vlad

On 25.03.25 17:09, Joshua Colletta wrote:
> Hi all,
> 
> New to the mailing list, so let me know if there is a better place to 
> ask these sorts of questions in the future.
> 
> I am new to SCST, my project is essentially a modified Virtual Tape 
> Library. I am attempting to use the scst_user handler to "pump" scsi 
> commands from the kernels interface up to the userspace, where an 
> awaiting Cpp codebase will action them.
> 
> My problem however, is thus:
> 
> I cannot get device registration to work on the code end.
> 
> As I understand it, the code itself has to report to the backend that it 
> wishes to init the emulated device within the userspace. In order to do 
> this I am trying to follow the scst_user docs as closely as possible.
> 
> I am, however, running into: "Failed to register SCST device: Errno=22 
> (Invalid Argument) when calling my ioctl(scst_fd, SCST_USER_REGISTER_DEVICE)
> 
> Code snippet below:
> 
> int TapeEmulationCore::init_SCSI_User_Interface(int &scst_fd) {
> // Open SCST user interface
> scst_fd = open("/dev/scst_user", O_RDWR);
> if (scst_fd < 0) {
> std::cerr << "Failed to open SCST User interface: /dev/scst_user\n";
> return 1;
> }
> // Ensure the device descriptor is zeroed and properly aligned
> scst_user_dev_desc dev;
> std::cout << "Size of dev:" << sizeof(dev) << std::endl;
> memset(&dev, 0, sizeof(dev));// safe init
> 
> // Ensure version/license strings are in user-space memory
> alignas(8) char version_str[] = DEV_USER_VERSION;
> alignas(8) char license_str[] = "GPL";
> 
> // Assign required string pointers (as aligned_u64)
> dev.version_str = reinterpret_cast<aligned_u64>(version_str);
> dev.license_str = reinterpret_cast<aligned_u64>(license_str);
> 
> // Assign device identity
> strncpy(dev.name, "my_virtual_tape", sizeof(dev.name) - 1);
> strncpy(dev.sgv_name, dev.name, sizeof(dev.sgv_name) - 1);// use same 
> name for SGV cache
> 
> // Basic device config
> dev.type = TYPE_TAPE;
> dev.block_size = 512;
> 
> // SGV memory/cache config (basic, non-shared, default pooling)
> dev.sgv_shared = 0;
> dev.sgv_disable_clustered_pool = 0;
> dev.sgv_single_alloc_pages = 0;
> dev.sgv_purge_interval = 0;
> 
> // Main device behavior options
> dev.opt.parse_type = SCST_USER_PARSE_CALL;
> dev.opt.on_free_cmd_type = SCST_USER_ON_FREE_CMD_IGNORE;
> dev.opt.memory_reuse_type = SCST_USER_MEM_NO_REUSE;
> dev.opt.partial_transfers_type = SCST_USER_PARTIAL_TRANSFERS_NOT_SUPPORTED;
> dev.opt.partial_len = 0;
> dev.opt.tst = 0;
> dev.opt.queue_alg = 0;
> dev.opt.tas = 0;
> dev.opt.swp = 0;
> dev.opt.d_sense = 0;
> dev.opt.has_own_order_mgmt = 0;
> 
> std::cout << "Size of filled dev: " << sizeof(dev) << std::endl;
> 
> 
> std::cout << "---- Dumping scst_user_dev_desc ----" << std::endl;
> std::cout << "version_str: " << reinterpret_cast<const 
> char*>(dev.version_str) << std::endl;
> std::cout << "license_str: " << reinterpret_cast<const 
> char*>(dev.license_str) << std::endl;
> std::cout << "name: " << dev.name << std::endl;
> std::cout << "sgv_name: " << dev.sgv_name << std::endl;
> std::cout << "type: " << (int)dev.type << std::endl;
> std::cout << "block_size: " << dev.block_size << std::endl;
> std::cout << "sgv_shared: " << (int)dev.sgv_shared << std::endl;
> std::cout << "disable_pool: " << (int)dev.sgv_disable_clustered_pool << 
> std::endl;
> std::cout << "single_alloc_pages: " << dev.sgv_single_alloc_pages << 
> std::endl;
> std::cout << "purge_interval: " << dev.sgv_purge_interval << std::endl;
> std::cout << "has_own_order_mgmt: " << (int)dev.opt.has_own_order_mgmt 
> << std::endl;
> std::cout << "opt.parse_type: " << (int)dev.opt.parse_type << std::endl;
> std::cout << "opt.mem_reuse_type: " << (int)dev.opt.memory_reuse_type << 
> std::endl;
> 
> // Register the device
> if (ioctl(scst_fd, SCST_USER_REGISTER_DEVICE, &dev) < 0) {
> std::cerr << "Failed to register SCST device: errno=" << errno << " (" 
> << strerror(errno) << ")" << "\n";
> close(scst_fd);
> return 1;
> }
> 
> Which in returns the following:
> 
> image.png
> 
> I apologise for dumping code. It struck me that this was likely an 
> alignment problem? I was wondering if someone with experience with the 
> scst_user handler could help me? Or perhaps, if it's easier, had a 
> minimal setup example I could use as reference?
> 
> Many thanks in advance,
> 
> Josh Colletta
> 
> 
> 
> 
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