new helper: iov_iter_get_pages_alloc()

same as iov_iter_get_pages(), except that pages array is allocated
(kmalloc if possible, vmalloc if that fails) and left for caller to
free.  Lustre and NFS ->direct_IO() switched to it.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 40 insertions, 0 deletions

diff --git a/mm/iov_iter.c b/mm/iov_iter.c
index 0b677f8f9bad..a5c691c1a283 100644
--- a/mm/iov_iter.c
+++ b/mm/iov_iter.c
@@ -1,6 +1,8 @@
 #include <linux/export.h>
 #include <linux/uio.h>
 #include <linux/pagemap.h>
+#include <linux/slab.h>
+#include <linux/vmalloc.h>
 
 size_t copy_page_to_iter(struct page *page, size_t offset, size_t bytes,
                          struct iov_iter *i)
@@ -263,6 +265,44 @@ ssize_t iov_iter_get_pages(struct iov_iter *i,
 }
 EXPORT_SYMBOL(iov_iter_get_pages);
 
+ssize_t iov_iter_get_pages_alloc(struct iov_iter *i,
+                   struct page ***pages, size_t maxsize,
+                   size_t *start)
+{
+        size_t offset = i->iov_offset;
+        const struct iovec *iov = i->iov;
+        size_t len;
+        unsigned long addr;
+        void *p;
+        int n;
+        int res;
+
+        len = iov->iov_len - offset;
+        if (len > i->count)
+                len = i->count;
+        if (len > maxsize)
+                len = maxsize;
+        addr = (unsigned long)iov->iov_base + offset;
+        len += *start = addr & (PAGE_SIZE - 1);
+        addr &= ~(PAGE_SIZE - 1);
+        n = (len + PAGE_SIZE - 1) / PAGE_SIZE;
+        
+        p = kmalloc(n * sizeof(struct page *), GFP_KERNEL);
+        if (!p)
+                p = vmalloc(n * sizeof(struct page *));
+        if (!p)
+                return -ENOMEM;
+
+        res = get_user_pages_fast(addr, n, (i->type & WRITE) != WRITE, p);
+        if (unlikely(res < 0)) {
+                kvfree(p);
+                return res;
+        }
+        *pages = p;
+        return (res == n ? len : res * PAGE_SIZE) - *start;
+}
+EXPORT_SYMBOL(iov_iter_get_pages_alloc);
+
 int iov_iter_npages(const struct iov_iter *i, int maxpages)
 {
         size_t offset = i->iov_offset;