0f670829a3
ioctl contants are platform dependent. It should be the same on
x86, aarch64 and s390x but it is indeed different on ppc64le.
This lead to the call to `ioctl_blockdev_flushbuf` actually
raising an exception of `OSError: [Errno 22] Invalid argument`.
The constant was calculated with a little python snippet that
in theory could also go directly into the code, but for now
the simpler condition in this patch is enough.
The snippet is a port of the defines from the Linux kernel,
specifically /usr/include/asm-generic/ioctl.h.
class IOConstants:
"""IO Commands for Linux"""
if platform.machine() == "ppc64le":
NRBITS = 8
TYPEBITS = 8
SIZEBITS = 13
DIR_NONE = 1
else:
NRBITS = 8
TYPEBITS = 8
SIZEBITS = 14
DIR_NONE = 0
NRSHIFT = 0
TYPESHIFT = NRSHIFT+NRBITS
SIZESHIFT = TYPESHIFT+TYPEBITS
DIRSHIFT = SIZESHIFT+SIZEBITS
@classmethod
def make(cls, directory, iotype, nr, size):
return ((directory << cls.DIRSHIFT) |
(iotype << cls.TYPESHIFT) |
(nr << cls.NRSHIFT) |
(size << cls.SIZESHIFT))
@classmethod
def make_dir_none(cls, iotype, nr):
return cls.make(cls.DIR_NONE, iotype, nr, 0)
This is used to get the value for `BLKFLSBUF` taken from the
include `/usr/include/linux/fs.h`:
#define BLKFLSBUF _IO(0x12,97) /* flush buffer cache */
The value is then obtained via:
print("0x%x" % IOConstants.make_dir_none(0x12,97))
0x20001261
123 lines
3 KiB
Python
123 lines
3 KiB
Python
"""Linux API Access
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This module provides access to linux system-calls and other APIs, in particular
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those not provided by the python standard library. The idea is to provide
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universal wrappers with broad access to linux APIs. Convenience helpers and
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higher-level abstractions are beyond the scope of this module.
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In some cases it is overly complex to provide universal access to a specific
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API. Hence, the API might be restricted to a reduced subset of its
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functionality, just to make sure we can actually implement the wrappers in a
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reasonable manner.
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"""
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import array
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import fcntl
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import platform
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__all__ = [
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"ioctl_get_immutable",
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"ioctl_toggle_immutable",
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]
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# NOTE: These are wrong on at least ALPHA and SPARC. They use different
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# ioctl number setups. We should fix this, but this is really awkward
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# in standard python.
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# Our tests will catch this, so we will not accidentally run into this
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# on those architectures.
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FS_IOC_GETFLAGS = 0x80086601
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FS_IOC_SETFLAGS = 0x40086602
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FS_IMMUTABLE_FL = 0x00000010
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if platform.machine() == "ppc64le":
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BLK_IOC_FLSBUF = 0x20001261
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else:
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BLK_IOC_FLSBUF = 0x00001261
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def ioctl_get_immutable(fd: int):
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"""Query FS_IMMUTABLE_FL
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This queries the `FS_IMMUTABLE_FL` flag on a specified file.
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Arguments
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---------
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fd
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File-descriptor to operate on.
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Returns
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-------
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bool
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Whether the `FS_IMMUTABLE_FL` flag is set or not.
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Raises
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------
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OSError
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If the underlying ioctl fails, a matching `OSError` will be raised.
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"""
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if not isinstance(fd, int) or fd < 0:
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raise ValueError()
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flags = array.array('L', [0])
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fcntl.ioctl(fd, FS_IOC_GETFLAGS, flags, True)
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return bool(flags[0] & FS_IMMUTABLE_FL)
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def ioctl_toggle_immutable(fd: int, set_to: bool):
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"""Toggle FS_IMMUTABLE_FL
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This toggles the `FS_IMMUTABLE_FL` flag on a specified file. It can both set
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and clear the flag.
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Arguments
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---------
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fd
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File-descriptor to operate on.
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set_to
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Whether to set the `FS_IMMUTABLE_FL` flag or not.
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Raises
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------
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OSError
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If the underlying ioctl fails, a matching `OSError` will be raised.
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"""
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if not isinstance(fd, int) or fd < 0:
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raise ValueError()
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flags = array.array('L', [0])
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fcntl.ioctl(fd, FS_IOC_GETFLAGS, flags, True)
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if set_to:
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flags[0] |= FS_IMMUTABLE_FL
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else:
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flags[0] &= ~FS_IMMUTABLE_FL
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fcntl.ioctl(fd, FS_IOC_SETFLAGS, flags, False)
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def ioctl_blockdev_flushbuf(fd: int):
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"""Flush the block device buffer cache
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NB: This function needs the `CAP_SYS_ADMIN` capability.
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Arguments
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---------
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fd
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File-descriptor of a block device to operate on.
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Raises
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------
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OSError
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If the underlying ioctl fails, a matching `OSError`
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will be raised.
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"""
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if not isinstance(fd, int) or fd < 0:
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raise ValueError(f"Invalid file descriptor: '{fd}'")
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fcntl.ioctl(fd, BLK_IOC_FLSBUF, 0)
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