[Bug 251035] [zfs][patch] allow 64 bit zfs to support 32 bit ioctls (Wine)

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=251035

            Bug ID: 251035
           Summary: [zfs][patch] allow 64 bit zfs to support 32 bit ioctls
                    (Wine)
           Product: Base System
           Version: 12.2-RELEASE
          Hardware: Any
                OS: Any
            Status: New
          Severity: Affects Some People
          Priority: ---
         Component: kern
          Assignee: bugs at FreeBSD.org
          Reporter: damjan.jov at gmail.com

Created attachment 219540
  --> https://bugs.freebsd.org/bugzilla/attachment.cgi?id=219540&action=edit
convert 32 bit zfs_iocparm_t to 64 bit

When 32 bit applications use libzfs to access ZFS data, they always fail in
zfs_open(), with 32 bit "zfs list" and "zpool list" crashing.

This is because
/usr/src/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zfs_ioctl.c function
zfsdev_ioctl() checks for:

---snip---
if (len != sizeof(zfs_iocparm_t)) {
---snip---

On amd64, sizeof(zfs_iocparm_t) is 24, as in
/usr/src/sys/cddl/contrib/opensolaris/common/zfs/zfs_ioctl_compat.h we have:

---snip---
typedef struct zfs_iocparm {
        uint32_t        zfs_ioctl_version;
        uint64_t        zfs_cmd;
        uint64_t        zfs_cmd_size;
} zfs_iocparm_t;
---snip---

which has its fields aligned to 8 byte boundaries. On i386, they are aligned to
4 byte boundaries, sizeof(zfs_iocparm_t) is only 20, and every ioctl fails with
EINVAL.

This affects Wine as it runs many 32 bit apps. Since Windows is
case-insensitive, Wine has to slowly scan the entire directory when doing file
I/O on a case-sensitive filesystem, to match filenames case-insensitively. ZFS
can create filesystems with casesensitivity=insensitive, allowing Wine to skip
the slow scan and speeding up file I/O considerably for some apps. When
developing a patch to Wine to check that casesensitivity property and use it
when insensitive (https://source.winehq.org/patches/data/195726) I noticed
zfs_open() always fails, which led me to this bug.

The attached patch correctly converts the 32 bit zfs_iocparm_t to 64 bit, and
allows at least Wine to work correctly. I haven't yet had a chance to test
whether it fixes 32 bit versions of the "zpool" and "zfs" tools (which probably
use more elaborate ioctls).

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