__GET_USER_PAGES(9) Memory Management in Linux __GET_USER_PAGES(9)NAME__get_user_pages - pin user pages in memory
SYNOPSIS
long __get_user_pages(struct task_struct * tsk, struct mm_struct * mm,
unsigned long start, unsigned long nr_pages,
unsigned int gup_flags, struct page ** pages,
struct vm_area_struct ** vmas,
int * nonblocking);
ARGUMENTS
tsk
task_struct of target task
mm
mm_struct of target mm
start
starting user address
nr_pages
number of pages from start to pin
gup_flags
flags modifying pin behaviour
pages
array that receives pointers to the pages pinned. Should be at
least nr_pages long. Or NULL, if caller only intends to ensure the
pages are faulted in.
vmas
array of pointers to vmas corresponding to each page. Or NULL if
the caller does not require them.
nonblocking
whether waiting for disk IO or mmap_sem contention
DESCRIPTION
Returns number of pages pinned. This may be fewer than the number
requested. If nr_pages is 0 or negative, returns 0. If no pages were
pinned, returns -errno. Each page returned must be released with a
put_page call when it is finished with. vmas will only remain valid
while mmap_sem is held.
Must be called with mmap_sem held for read or write.
__get_user_pages walks a process's page tables and takes a reference to
each struct page that each user address corresponds to at a given
instant. That is, it takes the page that would be accessed if a user
thread accesses the given user virtual address at that instant.
This does not guarantee that the page exists in the user mappings when
__get_user_pages returns, and there may even be a completely different
page there in some cases (eg. if mmapped pagecache has been invalidated
and subsequently re faulted). However it does guarantee that the page
won't be freed completely. And mostly callers simply care that the page
contains data that was valid *at some point in time*. Typically, an IO
or similar operation cannot guarantee anything stronger anyway because
locks can't be held over the syscall boundary.
If gup_flags & FOLL_WRITE == 0, the page must not be written to. If the
page is written to, set_page_dirty (or set_page_dirty_lock, as
appropriate) must be called after the page is finished with, and before
put_page is called.
If nonblocking != NULL, __get_user_pages will not wait for disk IO or
mmap_sem contention, and if waiting is needed to pin all pages,
*nonblocking will be set to 0.
In most cases, get_user_pages or get_user_pages_fast should be used
instead of __get_user_pages. __get_user_pages should be used only if
you need some special gup_flags.
COPYRIGHTKernel Hackers Manual 3.11 November 2013 __GET_USER_PAGES(9)
