cifs: Fix support for WSL-style symlinks

MS-FSCC in section 2.1.2.7 LX SYMLINK REPARSE_DATA_BUFFER now contains
documentation about WSL symlink reparse point buffers.

https://learn.microsoft.com/en

cifs: Fix support for WSL-style symlinks

MS-FSCC in section 2.1.2.7 LX SYMLINK REPARSE_DATA_BUFFER now contains
documentation about WSL symlink reparse point buffers.

https://learn.microsoft.com/en-us/openspecs/windows_protocols/ms-fscc/68337353-9153-4ee1-ac6b-419839c3b7ad

Fix the struct reparse_wsl_symlink_data_buffer to reflect buffer fields
according to the MS-FSCC documentation.

Fix the Linux SMB client to correctly fill the WSL symlink reparse point
buffer when creaing new WSL-style symlink. There was a mistake during
filling the data part of the reparse point buffer. It should starts with
bytes "\x02\x00\x00\x00" (which represents version 2) but this constant was
written as number 0x02000000 encoded in little endian, which resulted bytes
"\x00\x00\x00\x02". This change is fixing this mistake.

Fixes: 4e2043be5c14 ("cifs: Add support for creating WSL-style symlinks")
Signed-off-by: Pali Rohár <[email protected]>
Signed-off-by: Steve French <[email protected]>

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smb: client: Store original IO parameters and prevent zero IO sizes

During mount option processing and negotiation with the server, the
original user-specified rsize/wsize values were being modified

smb: client: Store original IO parameters and prevent zero IO sizes

During mount option processing and negotiation with the server, the
original user-specified rsize/wsize values were being modified directly.
This makes it impossible to recover these values after a connection
reset, leading to potential degraded performance after reconnection.

The other problem is that When negotiating read and write sizes, there are
cases where the negotiated values might calculate to zero, especially
during reconnection when server->max_read or server->max_write might be
reset. In general, these values come from the negotiation response.
According to MS-SMB2 specification, these values should be at least 65536
bytes.

This patch improves IO parameter handling:

1. Adds vol_rsize and vol_wsize fields to store the original user-specified
values separately from the negotiated values
2. Uses got_rsize/got_wsize flags to determine if values were
user-specified rather than checking for non-zero values, which is more
reliable
3. Adds a prevent_zero_iosize() helper function to ensure IO sizes are
never negotiated down to zero, which could happen in edge cases like
when server->max_read/write is zero

The changes make the CIFS client more resilient to unusual server
responses and reconnection scenarios, preventing potential failures
when IO sizes are calculated to be zero.

Signed-off-by: Wang Zhaolong <[email protected]>
Signed-off-by: Steve French <[email protected]>

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