tmpfs: support fallocate FALLOC_FL_PUNCH_HOLE

tmpfs has supported hole-punching since 2.6.16, via
madvise(,,MADV_REMOVE).

But nowadays fallocate(,FALLOC_FL_PUNCH_HOLE|FALLOC_FL_KEEP_SIZE,,) is
the agreed way to punch holes.

So add shmem_fallocate() to support that, and tweak shmem_truncate_range()
to support partial pages at both the beginning and end of range (never
needed for madvise, which demands rounded addr and rounds up length).

Based-on-patch-by: Cong Wang <amwang@redhat.com>
Signed-off-by: Hugh Dickins <hughd@google.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Cong Wang <amwang@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 57 insertions, 11 deletions

diff --git a/mm/shmem.c b/mm/shmem.c
index 45c26476f0fc..7e54ff1c63e1 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -53,6 +53,7 @@ static struct vfsmount *shm_mnt;
 #include <linux/blkdev.h>
 #include <linux/pagevec.h>
 #include <linux/percpu_counter.h>
+#include <linux/falloc.h>
 #include <linux/splice.h>
 #include <linux/security.h>
 #include <linux/swapops.h>
@@ -432,21 +433,23 @@ void shmem_truncate_range(struct inode *inode, loff_t lstart, loff_t lend)
         struct address_space *mapping = inode->i_mapping;
         struct shmem_inode_info *info = SHMEM_I(inode);
         pgoff_t start = (lstart + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
-        unsigned partial = lstart & (PAGE_CACHE_SIZE - 1);
-        pgoff_t end = (lend >> PAGE_CACHE_SHIFT);
+        pgoff_t end = (lend + 1) >> PAGE_CACHE_SHIFT;
+        unsigned int partial_start = lstart & (PAGE_CACHE_SIZE - 1);
+        unsigned int partial_end = (lend + 1) & (PAGE_CACHE_SIZE - 1);
         struct pagevec pvec;
         pgoff_t indices[PAGEVEC_SIZE];
         long nr_swaps_freed = 0;
         pgoff_t index;
         int i;
 
-        BUG_ON((lend & (PAGE_CACHE_SIZE - 1)) != (PAGE_CACHE_SIZE - 1));
+        if (lend == -1)
+                end = -1;       /* unsigned, so actually very big */
 
         pagevec_init(&pvec, 0);
         index = start;
-        while (index <= end) {
+        while (index < end) {
                 pvec.nr = shmem_find_get_pages_and_swap(mapping, index,
-                        min(end - index, (pgoff_t)PAGEVEC_SIZE - 1) + 1,
+                                min(end - index, (pgoff_t)PAGEVEC_SIZE),
                                                         pvec.pages, indices);
                 if (!pvec.nr)
                         break;
@@ -455,7 +458,7 @@ void shmem_truncate_range(struct inode *inode, loff_t lstart, loff_t lend)
                         struct page *page = pvec.pages[i];
 
                         index = indices[i];
-                        if (index > end)
+                        if (index >= end)
                                 break;
 
                         if (radix_tree_exceptional_entry(page)) {
@@ -479,22 +482,39 @@ void shmem_truncate_range(struct inode *inode, loff_t lstart, loff_t lend)
                 index++;
         }
 
-        if (partial) {
+        if (partial_start) {
                 struct page *page = NULL;
                 shmem_getpage(inode, start - 1, &page, SGP_READ, NULL);
                 if (page) {
-                        zero_user_segment(page, partial, PAGE_CACHE_SIZE);
+                        unsigned int top = PAGE_CACHE_SIZE;
+                        if (start > end) {
+                                top = partial_end;
+                                partial_end = 0;
+                        }
+                        zero_user_segment(page, partial_start, top);
+                        set_page_dirty(page);
+                        unlock_page(page);
+                        page_cache_release(page);
+                }
+        }
+        if (partial_end) {
+                struct page *page = NULL;
+                shmem_getpage(inode, end, &page, SGP_READ, NULL);
+                if (page) {
+                        zero_user_segment(page, 0, partial_end);
                         set_page_dirty(page);
                         unlock_page(page);
                         page_cache_release(page);
                 }
         }
+        if (start >= end)
+                return;
 
         index = start;
         for ( ; ; ) {
                 cond_resched();
                 pvec.nr = shmem_find_get_pages_and_swap(mapping, index,
-                        min(end - index, (pgoff_t)PAGEVEC_SIZE - 1) + 1,
+                                min(end - index, (pgoff_t)PAGEVEC_SIZE),
                                                         pvec.pages, indices);
                 if (!pvec.nr) {
                         if (index == start)
@@ -502,7 +522,7 @@ void shmem_truncate_range(struct inode *inode, loff_t lstart, loff_t lend)
                         index = start;
                         continue;
                 }
-                if (index == start && indices[0] > end) {
+                if (index == start && indices[0] >= end) {
                         shmem_deswap_pagevec(&pvec);
                         pagevec_release(&pvec);
                         break;
@@ -512,7 +532,7 @@ void shmem_truncate_range(struct inode *inode, loff_t lstart, loff_t lend)
                         struct page *page = pvec.pages[i];
 
                         index = indices[i];
-                        if (index > end)
+                        if (index >= end)
                                 break;
 
                         if (radix_tree_exceptional_entry(page)) {
@@ -1578,6 +1598,31 @@ static ssize_t shmem_file_splice_read(struct file *in, loff_t *ppos,
         return error;
 }
 
+static long shmem_fallocate(struct file *file, int mode, loff_t offset,
+                                                         loff_t len)
+{
+        struct inode *inode = file->f_path.dentry->d_inode;
+        int error = -EOPNOTSUPP;
+
+        mutex_lock(&inode->i_mutex);
+
+        if (mode & FALLOC_FL_PUNCH_HOLE) {
+                struct address_space *mapping = file->f_mapping;
+                loff_t unmap_start = round_up(offset, PAGE_SIZE);
+                loff_t unmap_end = round_down(offset + len, PAGE_SIZE) - 1;
+
+                if ((u64)unmap_end > (u64)unmap_start)
+                        unmap_mapping_range(mapping, unmap_start,
+                                            1 + unmap_end - unmap_start, 0);
+                shmem_truncate_range(inode, offset, offset + len - 1);
+                /* No need to unmap again: hole-punching leaves COWed pages */
+                error = 0;
+        }
+
+        mutex_unlock(&inode->i_mutex);
+        return error;
+}
+
 static int shmem_statfs(struct dentry *dentry, struct kstatfs *buf)
 {
         struct shmem_sb_info *sbinfo = SHMEM_SB(dentry->d_sb);
@@ -2490,6 +2535,7 @@ static const struct file_operations shmem_file_operations = {
         .fsync          = noop_fsync,
         .splice_read    = shmem_file_splice_read,
         .splice_write   = generic_file_splice_write,
+        .fallocate      = shmem_fallocate,
 #endif
 };