FILE_MAILSLOT_QUERY_INFORMATION - NtDoc

Native API online documentation, based on the System Informer (formerly Process Hacker) phnt headers
#ifndef _NTIOAPI_H

typedef struct _FILE_MAILSLOT_QUERY_INFORMATION
{
    ULONG MaximumMessageSize;
    ULONG MailslotQuota;
    ULONG NextMessageSize;
    ULONG MessagesAvailable;
    LARGE_INTEGER ReadTimeout;
} FILE_MAILSLOT_QUERY_INFORMATION, *PFILE_MAILSLOT_QUERY_INFORMATION;

#endif

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This structure is documented in Windows Driver Kit.