This is a utility library providing access to the
mmap family of functions in a portable way. It should work on Posix and Windows systems.
mmap allows you to directly map a file into the address space of your process without having to manually read it into memory sequentially. Typically this is much more efficient for files that are larger than a few Kb.
The library offers access to the following functions:
It also provides a convenience macro called
with-mmap to perform safe, local mappings of files.
(mmap:with-mmap (addr fd size #p"/etc/lsb-release") (with-output-to-string (out) (loop for i from 0 below size for char = (code-char (cffi:mem-aref addr :char i)) do (write-char char out))))
- No documentation provided.
Map the given path or number of bytes into the address space. PATH can be either a pathname designator, or NIL. If it is NIL, an anonymous file is mapped and the MMAP flag list must include the flag :ANONYMOUS. If it is a path, then the contents of the given file on the file system are mapped into the address space. The file contents can then be read, written, or executed depending on the given flags as if normal memory was accessed. If the file is NIL or its size cannot be automatically determined, you must pass a valid SIZE. You may optionally pass an OFFSET (in bytes) into the file from which the mapping begins. If the map attempt fails, an error of type MMAP-ERROR is signalled. If the call succeeds, three values are returned: PTR --- A CFFI:FOREIGN-POINTER that points to the start of the place in memory where the file contents have been mapped. The contents should be placed in increasing address order, unless the flag :GROWS-DOWN is active. FD --- An opaque file descriptor. You should not touch this. SIZE --- The size of the region of memory that has been mapped in bytes. All three values need to be passed on to MUNMAP completely unchanged. Any change could cause severe issues. The three options OPEN, PROTECTION, and MMAP are lists of flags. Not all of those flags are portable, some are only allowed on Linux, some only on non- Windows systems. To indicate support, the flags are marked as EVERY, POSIX (non-Windows), LINUX, or WINDOWS. OPEN :READ --- [EVERY] Opens the file for read access. :WRITE --- [EVERY] Opens the file for write access. :CREATE --- [EVERY] Creates the file if it does not exist yet. :ENSURE-CREATE --- [EVERY] Creates the file if it does not exist yet and errors if it does. :TRUNCATE --- [EVERY] Truncates the file and replaces it if it exists. :DIRECT --- [EVERY] Causes system buffers to be bypassed. :FILE-SYNC --- [EVERY] Causes writes to the file to be flushed asap. :DATA-SYNC --- [POSIX] Similar to FILE-SYNC, but uses data integrity semantics rather than file integrity semantics. :DONT-CLAIM-TTY--- [POSIX] If the file is a tty and the process does not already have a controlling tty, this file will not become the process' controlling tty. :NON-BLOCK --- [POSIX] Attempt to open the file in non-blocking mode, causing operations on the fd to return asap. :NO-FOLLOW --- [LINUX] Errors if the file is a symlink. :ASYNC --- [LINUX] Enable signal driven IO. :DIRECTORY --- [LINUX] Errors if the file is not a directory. :LARGE-FILE --- [LINUX] Allows opening files with size not representable by a 32 bit unsigned integer. PROTECTION :READ --- [EVERY] Allows reading from the memory region. The OPEN flag :READ is required for this protection mode. This flag is required on windows. :WRITE --- [EVERY] Allows writing to the memory region. :EXEC --- [EVERY] Allows executing code in the memory region. :NONE --- [POSIX] Prevents accessing the memory region. MMAP :PRIVATE --- [EVERY] The underlying file is not changed if the memory area is written to. Copy-on-write is employed to ensure separation. :SHARED --- [EVERY] The underlying file is changed if the memory area is written to and the change will be visible to other processes. In this case the OPEN flag :WRITE must be specified. :ANONYMOUS --- [LINUX/WINDOWS] The path should be a number of bytes to map to memory. The memory region is then mapped against an "anonymous" file. :NO-RESERVE --- [LINUX] Don't reserve swap for this mapping. If memory runs out, a segfault will be generated instead. :LOCKED --- [LINUX] Locks the region to RAM, preventing it from being swapped out. :GROWS-DOWN --- [LINUX] Causes the memory region to be mapped with a decreasing address, like in a stack. :POPULATE --- [LINUX] Pre-populate the memory region with the file contents, which can help performance. :NON-BLOCK --- [LINUX] Only useful with :POPULATE -- do not perform a read-ahead. The default values for the flags are: :OPEN (:READ) :PROTECTION (:READ) :MMAP (:PRIVATE) Note that if you are intending to use MPROTECT to change the protection of the mapped file at a later date, you need to call MMAP with the maximal combination of protection flags first. If this is not the protection that you want to start out with, call MPROTECT with the correct combination immediately after. For instance, if you would like to start with (:READ) and later want to change it to (:READ :WRITE), call MMAP with (:READ :WRITE), and immediately after call MPROTECT with (:READ). See MUNMAP See WITH-MMAP See MMAP-ERROR See http://pubs.opengroup.org/onlinepubs/7908799/xsh/mmap.html See http://pubs.opengroup.org/onlinepubs/009604499/functions/stat.html See http://man7.org/linux/man-pages/man2/mmap.2.html See http://man7.org/linux/man-pages/man2/stat.2.html See https://docs.microsoft.com/en-us/windows/desktop/api/fileapi/nf-fileapi-createfilew See https://docs.microsoft.com/en-us/windows/desktop/api/fileapi/nf-fileapi-getfilesize See https://docs.microsoft.com/en-us/windows/desktop/api/winbase/nf-winbase-createfilemappinga See https://msdn.microsoft.com/en-us/library/windows/desktop/aa366761(v=vs.85).aspx
Changes the access protection of the mapped memory region. The values passed to this function must be the ones retrieved from a call to MMAP. The following protection flags are supported: :READ --- [EVERY] Allows reading from the memory region. The OPEN flag :READ is required for this protection mode. This flag is required on windows. :WRITE --- [EVERY] Allows writing to the memory region. :EXEC --- [EVERY] Allows executing code in the memory region. :NONE --- [POSIX] Prevents accessing the memory region. This function returns nothing useful. This function may signal an MMAP-ERROR in case the operating system notices a problem. See MMAP See MMAP-ERROR See http://pubs.opengroup.org/onlinepubs/9699919799/functions/mprotect.html See http://man7.org/linux/man-pages/man2/mprotect.2.html See https://msdn.microsoft.com/en-us/library/windows/desktop/aa366898(v=vs.85).aspx
Causes writes to the mapped file area to be written to disk. The values passed to this function must be the ones retrieved from a call to MMAP. The following flags are supported: :SYNC --- [EVERY] Writing is synchronous. A call to this function will not return until the data is flushed to disk. :ASYNC --- [EVERY] Writing is asynchronous and a call will return immediately. :INVALIDATE --- [POSIX] Asks to invalidate other mappings of the same file, ensuring the view is synchronised. This function returns nothing useful. This function may signal an MMAP-ERROR in case the operating system notices a problem. See MMAP See MMAP-ERROR See http://pubs.opengroup.org/onlinepubs/000095399/functions/msync.html See http://man7.org/linux/man-pages/man2/msync.2.html See https://msdn.microsoft.com/en-us/library/windows/desktop/aa366563(v=vs.85).aspx See https://docs.microsoft.com/en-us/windows/desktop/api/fileapi/nf-fileapi-flushfilebuffers
Unmaps the memory region, freeing the address space and its file. The values passed to this function must be the ones retrieved from a call to MMAP. Calling MUNMAP with the same values more than once will lead to undefined consequences and may very well corrupt your system to crash. The same goes for calling MUNMAP with values not directly returned by MMAP, calling it with changed values returned by MMAP, or attempting to dereference the PTR after a call to MUNMAP. This function returns nothing useful. This function may signal an MMAP-ERROR in case the operating system notices a problem. See MMAP See MMAP-ERROR See WITH-MMAP See http://pubs.opengroup.org/onlinepubs/9699919799/functions/mprotect.html See http://man7.org/linux/man-pages/man2/mprotect.2.html See https://msdn.microsoft.com/en-us/library/windows/desktop/aa366882(v=vs.85).aspx See https://msdn.microsoft.com/en-us/library/windows/desktop/ms724211(v=vs.85).aspx
The OS-specific error code returned for the mmap failure. See MMAP-ERROR
The (hopefully) user-readable error message for the mmap failure. See MMAP-ERROR
Map the file or number of bytes to a memory region within the body. This is a convenience macro that calls MMAP with the given arguments, binds the results to the variables ADDR, FD, and SIZE, and automatically ensures that MUNMAP is called with the correct values when the body is exited. It is safe to change the ADDR, FD, and SIZE bindings, though probably not very good style to do so. It is NOT safe to save the ADDR and SIZE values somewhere and use them outside of the dynamic scope of the body. Attempting to do so is very likely going to burn your process to the ground. See MMAP See MUNMAP