==== FSH_SEGALLOC ====

**Purpose**

This function allocates a GDT or LDT selector. The selector will have read/write access. An FSD may call this function.   

**Calling Sequence**

<code c>
int far pascal FSH_SEGALLOC(flags, cbSeg, pSel)

unsigned short flags;
unsigned long cbSeg;
unsigned short far * pSel;
</code>

**Where**

//flags// indicate GDT/LDT, protection ring, swappable/non-swappable.   

|Bit 0x0001 off |indicates GDT selector returned. |
|Bit 0x0001 on |indicates LDT selector returned. |
|Bit 0x0002 off |indicates non-swappable memory. |
|Bit 0x0002 on |indicates swappable memory. |
|Bits 13 and 14 |are the desired ring number.   |
|All other bits are reserved and must be zero.   ||

//cbSeg// is the length of the segment.   

//pSel// is the far address of the location where the allocated selector will be stored. 

**Returns**

If no error is detected, a zero error code is returned. If an error is detected, one of the following error codes is returned:   

  * ERROR_INTERRUPT -- the current thread received a signal. 
  * ERROR_INVALID_PARAMETER -- the reserved bits in flags are set or requested size is too large. 
  * ERROR_NOT_ENOUGH_MEMORY -- too much memory is allocated. 

**Remarks**

It is strongly suggested that FSDs allocate all their data at protection level 0 for maximum protection from user programs.   

GDT selectors are a scarce resource; the FSD must be prepared to expect an error for allocation of a GDT segment. The FSD should limit itself to a maximum of 10 GDT segments. It is suggested that a large segment be allocated for each type of data and divided into per-process records.   

//FSH_SEGALLOC// may block.   

Take care to avoid deadlocks between swappable segments and swapper requests.   

**Note**:   OS/2 does not validate input parameters. An FSD, therefore, should call //FSH_PROBEBUF// where appropriate.