diff options
Diffstat (limited to 'lib/libc/sys/mmap.2')
| -rw-r--r-- | lib/libc/sys/mmap.2 | 75 |
1 files changed, 51 insertions, 24 deletions
diff --git a/lib/libc/sys/mmap.2 b/lib/libc/sys/mmap.2 index 7313134..17a3603 100644 --- a/lib/libc/sys/mmap.2 +++ b/lib/libc/sys/mmap.2 @@ -31,7 +31,7 @@ .\" .\" @(#)mmap.2 8.4 (Berkeley) 5/11/95 .\" -.Dd "May 11, 1995" +.Dd May 11, 1995 .Dt MMAP 2 .Os BSD 4 .Sh NAME @@ -44,7 +44,7 @@ .Fn mmap "caddr_t addr" "size_t len" "int prot" "int flags" "int fd" "off_t offset" .Sh DESCRIPTION The -.Nm mmap +.Fn mmap function causes the pages starting at .Fa addr and continuing for at most @@ -113,7 +113,7 @@ parameter is ignored. Do not permit the system to select a different address than the one specified. If the specified address cannot be used, -.Nm mmap +.Fn mmap will fail. If MAP_FIXED is specified, .Fa addr @@ -124,7 +124,7 @@ Notify the kernel that the region may contain semaphores and that special handling may be necessary. .It Dv MAP_INHERIT Permit regions to be inherited across -.Xr exec 2 +.Xr execve 2 system calls. .It Dv MAP_PRIVATE Modifications are private. @@ -147,9 +147,9 @@ the file descriptor argument specifies a file or device to which swapping should be done. .Sh RETURN VALUES Upon successful completion, -.Nm mmap +.Fn mmap returns a pointer to the mapped region. -Otherwise, a value of -1 is returned and +Otherwise, a value of MAP_FAILED is returned and .Va errno is set to indicate the error. .Sh ERRORS @@ -179,25 +179,27 @@ was not open for writing. .Fa Fd is not a valid open file descriptor. .It Bq Er EINVAL -.\"One of -.\".Dv MAP_ANON -.\"or -.\".Dv MAP_FILE -.\"was not specified as part of the -.\".Fa flags -.\"parameter. .Dv MAP_FIXED was specified and the .Fa addr -parameter was not page aligned or was outside of the -valid address range for a process. -.Dv MAP_ANON was specified and +parameter was not page aligned, or part of the desired address space +resides out of the valid address space for a user process. +.It Bq Er EINVAL +.Fa Len +was negative. +.It Bq Er EINVAL +.Dv MAP_ANON +was specified and the +.Fa fd +parameter was not -1. +.It Bq Er EINVAL +.Dv MAP_ANON +has not been specified and .Fa fd -was not \-1. -.Fa Fd did not reference a regular or character special file. -.Fa Len -was less than zero. +.It Bq Er EINVAL +.Fa Offset +was not page-aligned. (See BUGS below.) .It Bq Er ENOMEM .Dv MAP_FIXED was specified and the @@ -206,9 +208,34 @@ parameter wasn't available. .Dv MAP_ANON was specified and insufficient memory was available. .Sh "SEE ALSO" -.Xr getpagesize 2 , +.Xr madvise 2 , +.Xr mincore 2 , +.Xr mlock 2 , +.Xr mprotect 2 , .Xr msync 2 , +.Xr munlock 2 , .Xr munmap 2 , -.Xr mprotect 2 , -.Xr madvise 2 , -.Xr mincore 2 +.Xr getpagesize 3 +.Sh BUGS +.Ar len +is limited to 2GB. Mmapping slightly more than 2GB doesn't work, but +it is possible to map a window of size (filesize % 2GB) for file sizes +of slightly less than 2G, 4GB, 6GB and 8GB. +.Pp +The limit is imposed for a variety of reasons. Most of them have to do +with +.Tn FreeBSD +not wanting to use 64 bit offsets in the VM system due to +the extreme performance penalty. So +.Tn FreeBSD +uses 32bit page indexes and +this gives +.Tn FreeBSD +a maximum of 8TB filesizes. It's actually bugs in +the filesystem code that causes the limit to be further restricted to +1TB (loss of precision when doing blockno calculations). +.Pp +Another reason for the 2GB limit is that filesystem metadata can +reside at negative offsets. +.Pp +We currently can only deal with page aligned file offsets. |
