proxmox-backup/src/tools/sgutils2.rs

//! Bindings for libsgutils2
//!
//! Incomplete, but we currently do not need more.
//!
//! See: `/usr/include/scsi/sg_pt.h`
//!
//! The SCSI Commands Reference Manual also contains some useful information.

use std::os::unix::io::AsRawFd;
use std::ptr::NonNull;

use anyhow::{bail, format_err, Error};
use endian_trait::Endian;
use serde::{Deserialize, Serialize};
use libc::{c_char, c_int};
use std::ffi::CStr;

use proxmox::tools::io::ReadExt;

#[derive(thiserror::Error, Debug)]
pub struct SenseInfo {
    pub sense_key: u8,
    pub asc: u8,
    pub ascq: u8,
}

impl std::fmt::Display for SenseInfo {

    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {

        let sense_text = SENSE_KEY_DESCRIPTIONS
            .get(self.sense_key as usize)
            .map(|s| String::from(*s))
            .unwrap_or_else(|| format!("Invalid sense {:02X}", self.sense_key));

        if self.asc == 0 && self.ascq == 0 {
            write!(f, "{}", sense_text)
        } else {
            let additional_sense_text = get_asc_ascq_string(self.asc, self.ascq);
            write!(f, "{}, {}", sense_text, additional_sense_text)
        }
    }
}

#[derive(thiserror::Error, Debug)]
pub enum ScsiError {
    #[error("{0}")]
    Error(#[from] Error),
    #[error("{0}")]
    Sense(#[from] SenseInfo),
}

impl From<std::io::Error> for ScsiError {
    fn from(error: std::io::Error) -> Self {
        Self::Error(error.into())
    }
}

// Opaque wrapper for sg_pt_base
#[repr(C)]
struct SgPtBase { _private: [u8; 0] }

#[repr(transparent)]
struct SgPt {
    raw: NonNull<SgPtBase>,
}

impl Drop for SgPt {
    fn drop(&mut self) {
        unsafe { destruct_scsi_pt_obj(self.as_mut_ptr()) };
    }
}

impl SgPt {
    fn new() -> Result<Self, Error> {
        Ok(Self {
            raw: NonNull::new(unsafe { construct_scsi_pt_obj() })
                .ok_or_else(|| format_err!("construct_scsi_pt_ob failed"))?,
        })
    }

    fn as_ptr(&self) -> *const SgPtBase {
        self.raw.as_ptr()
    }

    fn as_mut_ptr(&mut self) -> *mut SgPtBase {
        self.raw.as_ptr()
    }
}

/// Peripheral device type text (see `inquiry` command)
///
/// see [https://en.wikipedia.org/wiki/SCSI_Peripheral_Device_Type]
pub const PERIPHERAL_DEVICE_TYPE_TEXT: [&'static str; 32] = [
    "Disk Drive",
    "Tape Drive",
    "Printer",
    "Processor",
    "Write-once",
    "CD-ROM",  // 05h
    "Scanner",
    "Optical",
    "Medium Changer", // 08h
    "Communications",
    "ASC IT8",
    "ASC IT8",
    "RAID Array",
    "Enclosure Services",
    "Simplified direct-access",
    "Optical card reader/writer",
    "Bridging Expander",
    "Object-based Storage",
    "Automation/Drive Interface",
    "Security manager",
    "Reserved",
    "Reserved",
    "Reserved",
    "Reserved",
    "Reserved",
    "Reserved",
    "Reserved",
    "Reserved",
    "Reserved",
    "Reserved",
    "Reserved",
    "Unknown",
];

//  SENSE KEYS
pub const SENSE_KEY_NO_SENSE: u8        = 0x00;
pub const SENSE_KEY_RECOVERED_ERROR: u8 = 0x01;
pub const SENSE_KEY_NOT_READY: u8       = 0x02;
pub const SENSE_KEY_MEDIUM_ERROR: u8    = 0x03;
pub const SENSE_KEY_HARDWARE_ERROR: u8  = 0x04;
pub const SENSE_KEY_ILLEGAL_REQUEST: u8 = 0x05;
pub const SENSE_KEY_UNIT_ATTENTION: u8  = 0x06;
pub const SENSE_KEY_DATA_PROTECT: u8    = 0x07;
pub const SENSE_KEY_BLANK_CHECK: u8     = 0x08;
pub const SENSE_KEY_COPY_ABORTED: u8    = 0x0a;
pub const SENSE_KEY_ABORTED_COMMAND: u8 = 0x0b;
pub const SENSE_KEY_VOLUME_OVERFLOW: u8 = 0x0d;
pub const SENSE_KEY_MISCOMPARE: u8      = 0x0e;

/// Sense Key Descriptions
pub const SENSE_KEY_DESCRIPTIONS: [&'static str; 16] = [
    "No Sense",
    "Recovered Error",
    "Not Ready",
    "Medium Error",
    "Hardware Error",
    "Illegal Request",
    "Unit Attention",
    "Data Protect",
    "Blank Check",
    "Vendor specific",
    "Copy Aborted",
    "Aborted Command",
    "Equal",
    "Volume Overflow",
    "Miscompare",
    "Completed",
];

#[repr(C, packed)]
#[derive(Endian)]
// Standard Inquiry page - 36 bytes
struct InquiryPage {
    peripheral_type: u8,
    rmb: u8,
    version: u8,
    flags3: u8,
    additional_length: u8,
    flags5: u8,
    flags6: u8,
    flags7: u8,
    vendor: [u8; 8],
    product: [u8; 16],
    revision: [u8; 4],
}

#[repr(C, packed)]
#[derive(Endian, Debug)]
pub struct RequestSenseFixed {
    pub response_code: u8,
    obsolete: u8,
    pub flags2: u8,
    pub information: [u8;4],
    pub additional_sense_len: u8,
    pub command_specific_information: [u8;4],
    pub additional_sense_code: u8,
    pub additional_sense_code_qualifier: u8,
    pub field_replacable_unit_code: u8,
    pub sense_key_specific: [u8; 3],
}

#[repr(C, packed)]
#[derive(Endian, Debug)]
struct RequestSenseDescriptor{
    response_code: u8,
    sense_key: u8,
    additional_sense_code: u8,
    additional_sense_code_qualifier: u8,
    reserved: [u8;4],
    additional_sense_len: u8,
}

/// Inquiry result
#[derive(Serialize, Deserialize, Debug)]
pub struct InquiryInfo {
    /// Peripheral device type (0-31)
    pub peripheral_type: u8,
    /// Peripheral device type as string
    pub peripheral_type_text: String,
    /// Vendor
    pub vendor: String,
    /// Product
    pub product: String,
    /// Revision
    pub revision: String,
}

#[repr(C, packed)]
#[derive(Endian, Debug, Copy, Clone)]
pub struct ModeParameterHeader {
    pub mode_data_len: u16,
    pub medium_type: u8, // Note: medium_type amd density_code are not the same
    pub flags3: u8,
    reserved4: [u8;2],
    pub block_descriptior_len: u16,
}

impl ModeParameterHeader {

    pub fn buffer_mode(&self) -> u8 {
        (self.flags3 & 0b0111_0000) >> 4
    }

    pub fn set_buffer_mode(&mut self, buffer_mode: bool) {
        let mut mode = self.flags3 & 0b1_000_1111;
        if buffer_mode {
            mode |= 0b0_001_0000;
        }
        self.flags3 = mode;
    }

    pub fn write_protect(&self) -> bool {
        (self.flags3 & 0b1000_0000) != 0
    }
}

#[repr(C, packed)]
#[derive(Endian, Debug, Copy, Clone)]
/// SCSI ModeBlockDescriptor for Tape devices
pub struct ModeBlockDescriptor {
    pub density_code: u8,
    pub number_of_blocks: [u8;3],
    reserverd: u8,
    pub block_length: [u8; 3],
}

impl ModeBlockDescriptor {

    pub fn block_length(&self) -> u32 {
        ((self.block_length[0] as u32) << 16) +
            ((self.block_length[1] as u32) << 8) +
            (self.block_length[2] as u32)

    }

    pub fn set_block_length(&mut self, length: u32) -> Result<(), Error> {
        if length > 0x80_00_00 {
            bail!("block length '{}' is too large", length);
        }
        self.block_length[0] = ((length & 0x00ff0000) >> 16) as u8;
        self.block_length[1] = ((length & 0x0000ff00) >> 8) as u8;
        self.block_length[2] = (length & 0x000000ff) as u8;
        Ok(())
    }
}

pub const SCSI_PT_DO_START_OK:c_int = 0;
pub const SCSI_PT_DO_BAD_PARAMS:c_int = 1;
pub const SCSI_PT_DO_TIMEOUT:c_int = 2;

pub const SCSI_PT_RESULT_GOOD:c_int = 0;
pub const SCSI_PT_RESULT_STATUS:c_int = 1;
pub const SCSI_PT_RESULT_SENSE:c_int = 2;
pub const SCSI_PT_RESULT_TRANSPORT_ERR:c_int = 3;
pub const SCSI_PT_RESULT_OS_ERR:c_int = 4;

#[link(name = "sgutils2")]
extern "C" {

    #[allow(dead_code)]
    fn scsi_pt_open_device(
        device_name: * const c_char,
        read_only: bool,
        verbose: c_int,
    ) -> c_int;

    fn sg_is_scsi_cdb(
        cdbp: *const u8,
        clen: c_int,
    ) -> bool;

    fn construct_scsi_pt_obj() -> *mut SgPtBase;
    fn destruct_scsi_pt_obj(objp: *mut SgPtBase);

    fn set_scsi_pt_data_in(
        objp: *mut SgPtBase,
        dxferp: *mut u8,
        dxfer_ilen: c_int,
    );

    fn set_scsi_pt_data_out(
        objp: *mut SgPtBase,
        dxferp: *const u8,
        dxfer_olen: c_int,
    );

    fn set_scsi_pt_cdb(
        objp: *mut SgPtBase,
        cdb: *const u8,
        cdb_len: c_int,
    );

    fn set_scsi_pt_sense(
        objp: *mut SgPtBase,
        sense: *mut u8,
        max_sense_len: c_int,
    );

    fn do_scsi_pt(
        objp: *mut SgPtBase,
        fd: c_int,
        timeout_secs: c_int,
        verbose: c_int,
    ) -> c_int;

    fn get_scsi_pt_resid(objp: *const SgPtBase) -> c_int;

    fn get_scsi_pt_sense_len(objp: *const SgPtBase) -> c_int;

    fn get_scsi_pt_status_response(objp: *const SgPtBase) -> c_int;

    fn get_scsi_pt_result_category(objp: *const SgPtBase) -> c_int;

    fn get_scsi_pt_os_err(objp: *const SgPtBase) -> c_int;

    fn sg_get_asc_ascq_str(
        asc: c_int,
        ascq:c_int,
        buff_len: c_int,
        buffer: *mut c_char,
    ) -> * const c_char;
}

/// Safe interface to run RAW SCSI commands
pub struct SgRaw<'a, F> {
    file: &'a mut F,
    buffer: Box<[u8]>,
    sense_buffer: [u8; 32],
    timeout: i32,
}

/// Get the string associated with ASC/ASCQ values
pub fn get_asc_ascq_string(asc: u8, ascq: u8) -> String {

    let mut buffer = [0u8; 1024];
    let res = unsafe {
        sg_get_asc_ascq_str(
            asc as c_int,
            ascq as c_int,
            buffer.len() as c_int,
            buffer.as_mut_ptr() as * mut c_char,
        )
    };

    proxmox::try_block!({
        if res.is_null() { // just to be safe
            bail!("unexpected NULL ptr");
        }
        Ok(unsafe { CStr::from_ptr(res) }.to_str()?.to_owned())
    }).unwrap_or_else(|_err: Error| {
        format!("ASC={:02x}x, ASCQ={:02x}x", asc, ascq)
    })
}

/// Allocate a page aligned buffer
///
/// SG RAWIO commands needs page aligned transfer buffers.
pub fn alloc_page_aligned_buffer(buffer_size: usize) -> Result<Box<[u8]> , Error> {
    let page_size = unsafe { libc::sysconf(libc::_SC_PAGESIZE) } as usize;
    let layout = std::alloc::Layout::from_size_align(buffer_size, page_size)?;
    let dinp = unsafe { std::alloc::alloc_zeroed(layout) };
    if dinp.is_null() {
        bail!("alloc SCSI output buffer failed");
    }

    let buffer_slice = unsafe { std::slice::from_raw_parts_mut(dinp, buffer_size)};
    Ok(unsafe { Box::from_raw(buffer_slice) })
}

impl <'a, F: AsRawFd> SgRaw<'a, F> {

    /// Create a new instance to run commands
    ///
    /// The file must be a handle to a SCSI device.
    pub fn new(file: &'a mut F, buffer_size: usize) -> Result<Self, Error> {

        let buffer;

        if buffer_size > 0 {
            buffer = alloc_page_aligned_buffer(buffer_size)?;
        } else {
            buffer =  Box::new([]);
        }

        let sense_buffer = [0u8; 32];

        Ok(Self { file, buffer, sense_buffer, timeout: 0 })
    }

    /// Set the command timeout in seconds (0 means default (60 seconds))
    pub fn set_timeout(&mut self, seconds: usize) {
        if seconds > (i32::MAX as usize) {
            self.timeout = i32::MAX; // don't care about larger values
        } else {
            self.timeout = seconds as i32;
        }
    }

    // create new object with initialized data_in and sense buffer
    fn create_scsi_pt_obj(&mut self) -> Result<SgPt, Error> {

        let mut ptvp = SgPt::new()?;

        if self.buffer.len() > 0 {
            unsafe {
                set_scsi_pt_data_in(
                    ptvp.as_mut_ptr(),
                    self.buffer.as_mut_ptr(),
                    self.buffer.len() as c_int,
                )
            };
        }

        unsafe {
            set_scsi_pt_sense(
                ptvp.as_mut_ptr(),
                self.sense_buffer.as_mut_ptr(),
                self.sense_buffer.len() as c_int,
            )
        };

        Ok(ptvp)
    }

    fn do_scsi_pt_checked(&mut self, ptvp: &mut SgPt) -> Result<(), ScsiError> {

        let res = unsafe { do_scsi_pt(ptvp.as_mut_ptr(), self.file.as_raw_fd(), self.timeout, 0) };
        match res {
            SCSI_PT_DO_START_OK => { /* Ok */ },
            SCSI_PT_DO_BAD_PARAMS => return Err(format_err!("do_scsi_pt failed - bad pass through setup").into()),
            SCSI_PT_DO_TIMEOUT => return Err(format_err!("do_scsi_pt failed - timeout").into()),
            code if code < 0 => {
                let errno = unsafe { get_scsi_pt_os_err(ptvp.as_ptr()) };
                let err = nix::Error::from_errno(nix::errno::Errno::from_i32(errno));
                return Err(format_err!("do_scsi_pt failed with err {}", err).into());
            }
            unknown => return Err(format_err!("do_scsi_pt failed: unknown error {}", unknown).into()),
        }

        if res < 0 {
            let err = nix::Error::last();
            return Err(format_err!("do_scsi_pt failed  - {}", err).into());
        }
        if res != 0 {
            return Err(format_err!("do_scsi_pt failed {}", res).into());
        }

        let sense_len = unsafe { get_scsi_pt_sense_len(ptvp.as_ptr()) };

        let res_cat = unsafe { get_scsi_pt_result_category(ptvp.as_ptr()) };
        match res_cat {
            SCSI_PT_RESULT_GOOD => return Ok(()),
            SCSI_PT_RESULT_STATUS => {
                let status = unsafe { get_scsi_pt_status_response(ptvp.as_ptr()) };
                if status != 0 {
                    return Err(format_err!("unknown scsi error - status response {}", status).into());
                }
                return Ok(());
            }
            SCSI_PT_RESULT_SENSE => {
                if sense_len == 0 {
                    return Err(format_err!("scsi command failed, but got no sense data").into());
                }

                let code = self.sense_buffer[0] & 0x7f;

                let mut reader = &self.sense_buffer[..(sense_len as usize)];

                let sense = match code {
                    0x70 => {
                        let sense: RequestSenseFixed = unsafe { reader.read_be_value()? };
                        SenseInfo {
                            sense_key: sense.flags2 & 0xf,
                            asc: sense.additional_sense_code,
                            ascq: sense.additional_sense_code_qualifier,
                        }
                    }
                    0x72 => {
                        let sense: RequestSenseDescriptor = unsafe { reader.read_be_value()? };
                        SenseInfo {
                            sense_key: sense.sense_key & 0xf,
                            asc: sense.additional_sense_code,
                            ascq: sense.additional_sense_code_qualifier,
                        }
                    }
                    0x71 | 0x73 => {
                        return Err(format_err!("scsi command failed: received deferred Sense").into());
                    }
                    unknown => {
                        return Err(format_err!("scsi command failed: invalid Sense response code {:x}", unknown).into());
                    }
                };

                return Err(ScsiError::Sense(sense));
            }
            SCSI_PT_RESULT_TRANSPORT_ERR => return Err(format_err!("scsi command failed: transport error").into()),
            SCSI_PT_RESULT_OS_ERR => {
                let errno = unsafe { get_scsi_pt_os_err(ptvp.as_ptr()) };
                let err = nix::Error::from_errno(nix::errno::Errno::from_i32(errno));
                return Err(format_err!("scsi command failed with err {}", err).into());
            }
            unknown => return Err(format_err!("scsi command failed: unknown result category {}", unknown).into()),
        }
    }

    /// Run the specified RAW SCSI command
    pub fn do_command(&mut self, cmd: &[u8]) -> Result<&[u8], ScsiError> {

        if !unsafe { sg_is_scsi_cdb(cmd.as_ptr(), cmd.len() as c_int) } {
            return Err(format_err!("no valid SCSI command").into());
        }

        if self.buffer.len() < 16 {
            return Err(format_err!("input buffer too small").into());
        }

        let mut ptvp = self.create_scsi_pt_obj()?;

        unsafe {
            set_scsi_pt_cdb(
                ptvp.as_mut_ptr(),
                cmd.as_ptr(),
                cmd.len() as c_int,
            )
        };

        self.do_scsi_pt_checked(&mut ptvp)?;

        let resid = unsafe { get_scsi_pt_resid(ptvp.as_ptr()) } as usize;
        if resid > self.buffer.len() {
            return Err(format_err!("do_scsi_pt failed - got strange resid (value too big)").into());
        }
        let data_len = self.buffer.len() - resid;

        Ok(&self.buffer[..data_len])
    }

    /// Run the specified RAW SCSI command, use data as input buffer
    pub fn do_in_command<'b>(&mut self, cmd: &[u8], data: &'b mut [u8]) -> Result<&'b [u8], ScsiError> {

        if !unsafe { sg_is_scsi_cdb(cmd.as_ptr(), cmd.len() as c_int) } {
            return Err(format_err!("no valid SCSI command").into());
        }

        if data.len() == 0 {
            return Err(format_err!("got zero-sized input buffer").into());
        }

        let mut ptvp = self.create_scsi_pt_obj()?;

        unsafe {
            set_scsi_pt_data_in(
                ptvp.as_mut_ptr(),
                data.as_mut_ptr(),
                data.len() as c_int,
            );

            set_scsi_pt_cdb(
                ptvp.as_mut_ptr(),
                cmd.as_ptr(),
                cmd.len() as c_int,
            );
        };

        self.do_scsi_pt_checked(&mut ptvp)?;

        let resid = unsafe { get_scsi_pt_resid(ptvp.as_ptr()) } as usize;

        if resid > data.len() {
            return Err(format_err!("do_scsi_pt failed - got strange resid (value too big)").into());
        }
        let data_len = data.len() - resid;

        Ok(&data[..data_len])
    }

    /// Run dataout command
    ///
    /// Note: use alloc_page_aligned_buffer to alloc data transfer buffer
    pub fn do_out_command(&mut self, cmd: &[u8], data: &[u8]) -> Result<(), ScsiError> {

        if !unsafe { sg_is_scsi_cdb(cmd.as_ptr(), cmd.len() as c_int) } {
            return Err(format_err!("no valid SCSI command").into());
        }

        let page_size = unsafe { libc::sysconf(libc::_SC_PAGESIZE) } as usize;
        if ((data.as_ptr() as usize) & (page_size -1)) != 0 {
            return Err(format_err!("wrong transfer buffer alignment").into());
        }

        let mut ptvp = self.create_scsi_pt_obj()?;

        unsafe {
            set_scsi_pt_data_out(
                ptvp.as_mut_ptr(),
                data.as_ptr(),
                data.len() as c_int,
            );

            set_scsi_pt_cdb(
                ptvp.as_mut_ptr(),
                cmd.as_ptr(),
                cmd.len() as c_int,
            );
        };

        self.do_scsi_pt_checked(&mut ptvp)?;

        Ok(())
    }
}

// Useful helpers

/// Converts SCSI ASCII text into String, trim zero and spaces
pub fn scsi_ascii_to_string(data: &[u8]) -> String {
    String::from_utf8_lossy(data)
        .trim_matches(char::from(0))
        .trim()
        .to_string()
}

/// Read SCSI Inquiry page
///
/// Returns Product/Vendor/Revision and device type.
pub fn scsi_inquiry<F: AsRawFd>(
    file: &mut F,
) -> Result<InquiryInfo, Error> {

    let allocation_len: u8 = std::mem::size_of::<InquiryPage>() as u8;

    let mut sg_raw = SgRaw::new(file, allocation_len as usize)?;
    sg_raw.set_timeout(30); // use short timeout

    let mut cmd = Vec::new();
    cmd.extend(&[0x12, 0, 0, 0, allocation_len, 0]); // INQUIRY

    let data = sg_raw.do_command(&cmd)
        .map_err(|err| format_err!("SCSI inquiry failed - {}", err))?;

    proxmox::try_block!({
        let mut reader = &data[..];

        let page: InquiryPage  = unsafe { reader.read_be_value()? };

        let peripheral_type = page.peripheral_type & 31;

        let info = InquiryInfo {
            peripheral_type,
            peripheral_type_text: PERIPHERAL_DEVICE_TYPE_TEXT[peripheral_type as usize].to_string(),
            vendor: scsi_ascii_to_string(&page.vendor),
            product: scsi_ascii_to_string(&page.product),
            revision: scsi_ascii_to_string(&page.revision),
        };

        Ok(info)
    }).map_err(|err: Error| format_err!("decode inquiry page failed - {}", err))
}

/// Run SCSI Mode Sense
///
/// Warning: P needs to be repr(C, packed)]
pub fn scsi_mode_sense<F: AsRawFd, P: Endian>(
    file: &mut F,
    disable_block_descriptor: bool,
    page_code: u8,
    sub_page_code: u8,
) -> Result<(ModeParameterHeader, Option<ModeBlockDescriptor>, P), Error> {

    let allocation_len: u16 = 4096;
    let mut sg_raw = SgRaw::new(file, allocation_len as usize)?;

    let mut cmd = Vec::new();
    cmd.push(0x5A); // MODE SENSE(10)
    if disable_block_descriptor {
        cmd.push(8); // DBD=1 (Disable Block Descriptors)
    } else {
        cmd.push(0); // DBD=0 (Include Block Descriptors)
    }
    cmd.push(page_code & 63); // report current values for page_code
    cmd.push(sub_page_code);

    cmd.extend(&[0, 0, 0]); // reserved
    cmd.extend(&allocation_len.to_be_bytes()); // allocation len
    cmd.push(0); //control

    let data = sg_raw.do_command(&cmd)
        .map_err(|err| format_err!("mode sense failed - {}", err))?;

    proxmox::try_block!({
        let mut reader = &data[..];

        let head: ModeParameterHeader = unsafe { reader.read_be_value()? };

        if (head.mode_data_len as usize + 2) != data.len() {
            bail!("wrong mode_data_len");
        }

        if disable_block_descriptor && head.block_descriptior_len != 0 {
            bail!("wrong block_descriptior_len");
        }

        let mut block_descriptor: Option<ModeBlockDescriptor> = None;

        if !disable_block_descriptor {
            if head.block_descriptior_len != 8 {
                bail!("wrong block_descriptior_len");
            }

            block_descriptor = Some(unsafe { reader.read_be_value()? });
        }

        let page: P = unsafe { reader.read_be_value()? };

        Ok((head, block_descriptor, page))
    }).map_err(|err: Error| format_err!("decode mode sense failed - {}", err))
}

/// Resuqest Sense
pub fn scsi_request_sense<F: AsRawFd>(
    file: &mut F,
) -> Result<RequestSenseFixed, ScsiError> {

    // request 252 bytes, as mentioned in the Seagate SCSI reference
    let allocation_len: u8 = 252;

    let mut sg_raw = SgRaw::new(file,  allocation_len as usize)?;
    sg_raw.set_timeout(30); // use short timeout
    let mut cmd = Vec::new();
    cmd.extend(&[0x03, 0, 0, 0, allocation_len, 0]); // REQUEST SENSE FIXED FORMAT

    let data = sg_raw.do_command(&cmd)
        .map_err(|err| format_err!("request sense failed - {}", err))?;

    let sense = proxmox::try_block!({
        let data_len = data.len();

        if data_len < std::mem::size_of::<RequestSenseFixed>() {
            bail!("got short data len ({})", data_len);
        }
        let code = data[0] & 0x7f;
        if code != 0x70 {
            bail!("received unexpected sense code '0x{:02x}'", code);
        }

        let mut reader = &data[..];

        let sense: RequestSenseFixed = unsafe { reader.read_be_value()? };

        Ok(sense)
    }).map_err(|err: Error| format_err!("decode request sense failed - {}", err))?;

    Ok(sense)
}