8000 expand info/debug/warning msgs if USB device `serial_number` not readable by jllanfranchi · Pull Request #423 · pyvisa/pyvisa-py · GitHub
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expand info/debug/warning msgs if USB device serial_number not readable #423

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Merged
merged 4 commits into from
Apr 1, 2025
Merged

expand info/debug/warning msgs if USB device serial_number not readable #423

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1b731ca
expand info/debug/warning messages if USB device `serial_number` not …
jllanfranchi Apr 7, 2024
9fd7c38
Change message from USBTMC -> USB INSTR for clarity
jllanfranchi Apr 8, 2024
9c22f9e
usb: check permissions only on Linux and use appropriate logger method
MatthieuDartiailh Oct 28, 2024
e204804
docs: add more details regarding permissions in the docs
MatthieuDartiailh Mar 25, 2025
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8 changes: 7 additions & 1 deletion docs/source/installation.rst
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Expand Up @@ -69,7 +69,13 @@ details.

On Unix system, one may have to modify udev rules to allow non-root access to
the device you are trying to connect to. The following tutorial describes how
to do it http://ask.xmodulo.com/change-usb-device-permission-linux.html.
to do it https://www.xmodulo.com/change-usb-device-permission-linux.html.

Note that USBTMC devices show up as both /dev/usbtmcN and /dev/bus/usb/NNN/NNN.
Both instances need to have suitable permissions for pyvisa with pyvisa-py to
be able to communicate. If only the /dev/usbtmcN has permissions then you get::

WARNING Found a device whose serial number cannot be read

On Windows, you may have to uninstall the USBTMC-specific driver installed by
Windows and re-install a generic driver. Please check `libusb's guide`_ for more
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39 changes: 36 additions & 3 deletions pyvisa_py/usb.py
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Expand Up @@ -8,6 +8,10 @@
"""

import errno
import logging
import os
import sys
import traceback
from typing import Any, List, Tuple, Type, Union

from pyvisa import attributes, constants
Expand Down Expand Up @@ -272,9 +276,9 @@

try:
serial = dev.serial_number
except (NotImplementedError, ValueError):
except (NotImplementedError, ValueError) as err:

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pyvisa_py/usb.py#L279 

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msg = (
"Found a device whose serial number cannot be read."
"Found a USB INSTR device whose serial number cannot be read."
" The partial VISA resource name is: " + fmt
)
LOGGER.warning(
Expand All @@ -287,6 +291,35 @@
"usb_interface_number": intfc,
},
)
logging_level = LOGGER.getEffectiveLevel()

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if logging_level <= logging.DEBUG:
LOGGER.debug("Error while reading serial number", exc_info=err)

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elif logging_level <= logging.INFO:
if exc_strs := traceback.format_exception_only(err):
LOGGER.info(

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"Error raised from underlying module (pyusb): %s",
exc_strs[0].strip(),
)

# Check permissions on Linux
if sys.platform.startswith("linux"):
dev_path = f"/dev/bus/usb/{dev.bus:03d}/{dev.address:03d}"

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if os.path.exists(dev_path) and not os.access(dev_path, os.O_RDWR):
missing_perms = []

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if not os.access(dev_path, os.O_RDONLY):
missing_perms.append("read from")

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if not os.access(dev_path, os.O_WRONLY):
missing_perms.append("write to")
missing_perms_str = " or ".join(missing_perms)
LOGGER.warning(

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"User does not have permission to %s %s, so the above "
"USB INSTR device cannot be used by pyvisa; see"
" https://pyvisa.readthedocs.io/projects/pyvisa-py/en/latest/installation.html"
" for more info.",
missing_perms_str,
dev_path,
)

continue

out.append(
Expand Down Expand Up @@ -331,7 +364,7 @@
serial = dev.serial_number
except (NotImplementedError, ValueError, usb.USBError):
msg = (
"Found a device whose serial number cannot be read."
"Found a USB RAW device whose serial number cannot be read."
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can't we run into the same permissions issue here?

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We do. I thought pyvisa didn't care about RAW devices (because it doesn't control them), but I realize now that assumption may be incorrect.

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USB RAW are weird because there are supported by NI but are not part of the IVI specs. If we can provide more information we should though.

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I observed in pyvisa issue Linux host and getting permissions to talk to a USBTMC device
USBTMC devices show up as both /dev/usbtmcN and /dev/bus/usb/NNN/NNN
Both instances need to have suitable permissions for pyvisa with pyvisa-py to be able to communicate

If only the /dev/usbtmcN has permissions then you get WARNING Found a device whose serial number cannot be read

" The partial VISA resource name is: " + fmt
)
LOGGER.warning(
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