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util/linux: fix BLK_IOC_FLSBUF on ppc64le

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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
This commit is contained in:
Christian Kellner 2022-01-28 17:01:55 +00:00 • committed by Achilleas Koutsou
parent 087b403042
commit 0f670829a3
1 changed files with 6 additions and 1 deletions
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7
osbuild/util/linux.py
View file

@ -14,6 +14,7 @@ reasonable manner.
import array
import fcntl
import platform
__all__ = [
@ -32,7 +33,11 @@ FS_IOC_SETFLAGS = 0x40086602
FS_IMMUTABLE_FL = 0x00000010
BLK_IOC_FLSBUF = 0x00001261
if platform.machine() == "ppc64le":
BLK_IOC_FLSBUF = 0x20001261
else:
BLK_IOC_FLSBUF = 0x00001261
def ioctl_get_immutable(fd: int):