INT 2A,80 - Begin DOS Critical Section

AH = 80h

AL = critical section identifier (00-0F)

= 01 DOS kernel, SHARE.EXE and network data structure integrity

= 02 DOS kernel, device driver exclusivity

= 05 IFSFUNC (Installable File System, IFS, DOS 4.0+)

= 06 IFSFUNC (Installable File System, IFS, DOS 4.0+)

= 08 ASSIGN.COM

returns nothing

- indicates that the region of code being entered should not be

interrupted and identifies the critical region

- this function is not normally called by user applications but is

often hooked to monitor if DOS is in a critical section

- this information is necessary to reenter DOS using the swappable

data area returned by ~INT 21,5D~ subfunction 0B

- see ~Bibliography~ reference to "Undocumented DOS"