[PATCH] mmap zero-length hugetlb file with PROT_NONE to protect a hugetlb virtual area

Sometimes, applications need below call to be successful although
"/mnt/hugepages/file1" doesn't exist.

fd = open("/mnt/hugepages/file1", O_CREAT|O_RDWR, 0755);
*addr = mmap(NULL, 0x1024*1024*256, PROT_NONE, 0, fd, 0);

As for regular pages (or files), above call does work, but as for huge
pages, above call would fail because hugetlbfs_file_mmap would fail if
(!(vma->vm_flags & VM_WRITE) && len > inode->i_size).

This capability on huge page is useful on ia64 when the process wants to
protect one area on region 4, so other threads couldn't read/write this
area.  A famous JVM (Java Virtual Machine) implementation on IA64 needs the
capability.

Signed-off-by: Zhang Yanmin <[email protected]>
Cc: David Gibson <[email protected]>
Cc: Hugh Dickins <[email protected]>
[ Expand-on-mmap semantics again... this time matching normal fs's. wli ]
Acked-by: William Lee Irwin III <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

0 files changed, 0 insertions, 0 deletions