Passing Structures to OS/2 LAN Manager Remote API Calls (63541)

SYMPTOMS

A structure passed to NetShareAdd() includes pointers to ASCIIZ strings. To keep all the data in one place, the data for these strings was appended to the end of the structure (that is, the structure and the strings it addresses are kept in one physical buffer).

Since the buffer includes both the strings and the passed structure, the buffer length supplied must be the length of the structure plus the length of the appended strings. However, when the NetShareAdd() API is called from MS-DOS to add a share on a remote server, it returns an error of ERROR_INVALID_PARAMETER (number 87).

CAUSE

This characteristic applies to all the OS/2 LAN Manager Add or SetInfo type API calls; OS/2 LAN Manager uses an optimizing technique to minimize the amount of data actually sent on a remote API call (a call that is performed on another physical machine).

Any pointers in a passed structure that point to data within the structure itself are set to NULL. Since the code that transfers the API call handles many different APIs, OS/2 LAN Manager determines this by checking whether any pointers point to an area somewhere within where the structure starts and ends, as determined by the passed structure pointer and buffer length field. Since the buffer length includes more than just the structure length, OS/2 LAN Manager assumes that the pointers within the structure are pointing into the structure itself, and therefore sets them to NULL. This causes the parameters to become invalid.

RESOLUTION

The proper value to supply for the buffer-length argument to Add and SetInfo type OS/2 LAN Manager API calls is as follows

      sizeof(struct xxxxx)

where "xxxxx" is the name of the structure whose pointer is being passed. You can still place the structure and the data it addresses in the same buffer, just don't let OS/2 LAN Manager be aware of it.

Please note that this information applies to remote API calls only. More information on this topic can be found in Chapter 1 of the "Microsoft LAN Manager Programmer's Reference for OS/2 LAN Manager and MS-DOS LAN Manager."