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NAME    [Toc]    [Back]

     malloc - kernel memory allocator

SYNOPSIS    [Toc]    [Back]

     #include <sys/types.h>
     #include <sys/malloc.h>

     void *
     malloc(unsigned long size, int type, int flags);

     MALLOC(space,  cast,  unsigned  long  size,  int  type,  int

     free(void *addr, int type);

     FREE(void *addr, int type);

DESCRIPTION    [Toc]    [Back]

     The malloc() function allocates uninitialized memory in kernel address
     space for an object whose size is specified by size.  free()
     memory  at  address  addr  that  was previously allocated by
malloc() for reuse.
  The MALLOC() macro variant is functionally  equivalent

           (space) = (cast)malloc((u_long)(size), type, flags)

     and the FREE() macro variant is equivalent to

           free((caddr_t)(addr), type)

     These macros should only be used when the size argument is a

     Unlike its standard C library counterpart  (malloc(3)),  the
kernel version
     takes two more arguments.  The flags argument further qualifies
     malloc()'s operational characteristics as follows:

                Causes malloc() to return  NULL  if  the  request
cannot be immediately
 fulfilled due to resource shortage.  Otherwise,
                malloc() may call sleep to wait for resources  to
be released
                by  other  processes.   If  this flag is not set,
malloc() will
                never return NULL.  Note that M_WAITOK is  conveniently defined
                to be 0, and hence maybe or'ed into the flags argument to indicate
 that it's OK to wait for resources.

     Currently, only one flag is defined.

     The type argument broadly identifies  the  kernel  subsystem
for which the
     allocated  memory  was needed, and is commonly used to maintain statistics
     about kernel memory usage.  The following types are currently defined:

           M_FREE          Should be on free list.
           M_MBUF          Mbuf memory.
           M_DEVBUF        Device driver memory.
           M_DEBUG         malloc debug structures.
           M_PCB           Protocol control blocks.
           M_RTABLE        Routing tables.
           M_FTABLE        Fragment reassembly headers.
           M_IFADDR        Interface addresses.
           M_SOOPTS        Socket options.
           M_SYSCTL        Sysctl persistent buffers.
           M_NAMEI         Namei path name buffers.
           M_IOCTLOPS      Ioctl data buffers.
           M_IOV           Large IOVs.
           M_MOUNT         VFS mount structs.
           M_NFSREQ        NFS request headers.
           M_NFSMNT        NFS mount structures.
           M_NFSNODE       NFS vnode private part.
           M_VNODE         Dynamically allocated vnodes.
           M_CACHE         Dynamically allocated cache entries.
           M_DQUOT         UFS quota entries.
           M_UFSMNT        UFS mount structures.
           M_SHM            SVID  compatible  shared  memory segments.
           M_VMMAP         VM map structures.
           M_VMPMAP        VM pmap data.
           M_FILE          Open file structures.
           M_FILEDESC      Open file descriptor tables.
           M_PROC          Proc structures.
           M_SUBPROC       Proc sub-structures.
           M_VCLUSTER      Cluster for VFS.
           M_MFSNODE       MFS vnode private part.
           M_NETADDR       Export host address structures.
           M_NFSSVC        NFS server structures.
           M_NFSUID        NFS uid mapping structures.
           M_NFSD          NFS server daemon structures.
           M_IPMOPTS       Internet multicast options.
           M_IPMADDR       Internet multicast addresses.
           M_IFMADDR       Link-level multicast addresses.
           M_MRTABLE       Multicast routing tables.
           M_ISOFSMNT      ISOFS mount structures.
           M_ISOFSNODE     ISOFS vnode private part.
           M_MSDOSFSMNT    MSDOS FS mount structures.
           M_MSDOSFSFAT    MSDOS FS FAT tables.
           M_MSDOSFSNODE   MSDOS FS vnode private part.
           M_TTYS          Allocated tty structures.
           M_EXEC          Argument lists & other mem used by exec.
           M_MISCFSMNT     Misc. FS mount structures.
           M_ADOSFSMNT     ADOSFS mount structures.
           M_ANODE         ADOSFS anode structures and tables.
           M_ADOSFSBITMAP  ADOSFS bitmap.
           M_EXT2FSNODE    EXT2FS vnode private part.
           M_PFKEY         Pfkey data.
           M_TDB           Transforms database.
           M_XDATA         IPsec data.
           M_VFS           VFS file systems.
           M_PAGEDEP       File page dependencies.
           M_INODEDEP      Inode dependencies.
           M_NEWBLK        New block allocation.
           M_VMSWAP        VM swap structures.
           M_RAIDFRAME     RAIDframe data.
           M_UVMAMAP       UVM amap and related.
           M_UVMAOBJ       UVM aobj and related.
           M_USB           USB general.
           M_USBDEV        USB device driver.
           M_USBHC         USB host controller.
           M_MEMDESC       Memory range.
           M_UFS_EXTATTR   UFS Extended Attributes.
           M_CREDENTIALS   ipsec(4) related credentials.
           M_PACKET_TAGS   Packet-attached information tags.
           M1394CTL        IEEE 1394 control structures.
           M1394DATA       IEEE 1394 data buffers.
           M_EMULDATA      Per process emulation data.
           M_IP6OPT        IPv6 options.
           M_IP6NDP        IPv6 neighbour discovery structures.
           M_IP6RR         IPv6 router renumbering prefix.
           M_RR_ADDR         IPv6  router  renumbering  interface
           M_TEMP          Miscellaneous temporary data  buffers.
           M_NTFSMNT       NTFS mount structures.
           M_NTFSNTNODE    NTFS ntnode information.
           M_NTFSNODE      NTFS fnode information.
           M_NTFSDIR       NTFS directory buffers.
           M_NTFSHASH      NTFS ntnode hash tables.
           M_NTFSVATTR     NTFS file attribute information.
           M_NTFSRDATA     NTFS resident data.
           M_NTFSDECOMP     NTFS decompression temporary storage.
           M_NTFSRUN       NTFS vrun storage.

     Statistics based on the type argument are maintained only if
the kernel
     option  KMEMSTATS is used when compiling the kernel (the default in
     current OpenBSD kernels) and can be examined by  using  `vmstat -m'.

RETURN VALUES    [Toc]    [Back]

     malloc()  returns  a kernel virtual address that is suitably
aligned for
     storage of any type of object.

DIAGNOSTICS    [Toc]    [Back]

     A kernel compiled with the DIAGNOSTIC  configuration  option
attempts to
     detect  memory  corruption  caused by such things as writing
outside the allocated
 area and unbalanced calls to the malloc() and free()
     Failing  consistency  checks  will cause a panic or a system
console message:

           +o   panic: ``malloc - bogus type''
           +o   panic: ``malloc: out of space in kmem_map''
           +o   panic: ``malloc: allocation too large''
           +o   panic: ``malloc: wrong bucket''
           +o   panic: ``malloc: lost data''
           +o   panic: ``free: unaligned addr''
           +o   panic: ``free: duplicated free''
           +o   panic: ``free: multiple frees''
           +o    panic:  ``kmeminit:  minbucket  too  small/struct
freelist too
           +o   ``multiply freed item <addr>''
           +o   ``Data modified on freelist: <data object description>''

DEBUGGING    [Toc]    [Back]

     A kernel compiled with the MALLOC_DEBUG  option  allows  for
more extensive
     debugging of memory allocations.  The debug_malloc_type,
     debug_malloc_size,          debug_malloc_size_lo         and
debug_malloc_size_hi variables
 choose which allocation to  debug.   debug_malloc_type
should be set
     to  the  memory  type and debug_malloc_size should be set to
the memory size
     to   debug.    0   can    be    used    as    a    wildcard.
debug_malloc_size_lo and
     debug_malloc_size_hi can be used to specify a range of sizes
if the exact
     size  to  debug  is  not  known.   When  those   are   used,
debug_malloc_size needs
     to be set to the wildcard.  M_DEBUG can also be specified as
an allocation
 type to force allocation with debugging.

     Every call to malloc() with a  memory  type  and  size  that
matches the debugged
  type  and size will allocate two virtual pages.  The
pointer returned
 will be aligned so that the requested area  will  end
at the page
     boundary  and the second virtual page will be left unmapped.
This way we
     can catch reads and writes outside the allocated area.

     Every call to free() with memory that was  returned  by  the
debugging malloc
 will cause the memory area to become unmapped so that we
can catch
     dangling reads and writes to freed memory.

     There are no special diagnostics if any errors are caught by
the debugging
 malloc.  The errors will look like normal access to unmapped memory.
     On a memory access error, the show malloc command in  ddb(4)
can be invoked
  to see what memory areas are allocated and freed.  If
the faulting
     address is within two pages from an address on the allocated
list, there
     was  an  access outside the allocated area.  If the faulting
address is
     within two pages from an address on the free list, there was
an access to
     freed memory.

     Care  needs  to be taken when using the MALLOC_DEBUG option:
the memory
     consumption can run away pretty quickly and there is  a  severe performance
     degradation  when  allocating  and  freeing  debugged memory

SEE ALSO    [Toc]    [Back]


OpenBSD     3.6                           June      16,      1996
[ Back ]
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