fallocate should be a file operation

Currently all filesystems except XFS implement fallocate asynchronously,
while XFS forced a commit.  Both of these are suboptimal - in case of O_SYNC
I/O we really want our allocation on disk, especially for the !KEEP_SIZE
case where we actually grow the file with user-visible zeroes.  On the
other hand always commiting the transaction is a bad idea for fast-path
uses of fallocate like for example in recent Samba versions.   Given
that block allocation is a data plane operation anyway change it from
an inode operation to a file operation so that we have the file structure
available that lets us check for O_SYNC.

This also includes moving the code around for a few of the filesystems,
and remove the already unnedded S_ISDIR checks given that we only wire
up fallocate for regular files.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 113 insertions, 0 deletions

diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index 66836d85763b..a9e0a4eaf3d9 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -24,6 +24,7 @@
 #include <linux/string.h>
 #include <linux/backing-dev.h>
 #include <linux/mpage.h>
+#include <linux/falloc.h>
 #include <linux/swap.h>
 #include <linux/writeback.h>
 #include <linux/statfs.h>
@@ -1237,6 +1238,117 @@ static int btrfs_file_mmap(struct file	*filp, struct vm_area_struct *vma)
         return 0;
 }
 
+static long btrfs_fallocate(struct file *file, int mode,
+                            loff_t offset, loff_t len)
+{
+        struct inode *inode = file->f_path.dentry->d_inode;
+        struct extent_state *cached_state = NULL;
+        u64 cur_offset;
+        u64 last_byte;
+        u64 alloc_start;
+        u64 alloc_end;
+        u64 alloc_hint = 0;
+        u64 locked_end;
+        u64 mask = BTRFS_I(inode)->root->sectorsize - 1;
+        struct extent_map *em;
+        int ret;
+
+        alloc_start = offset & ~mask;
+        alloc_end =  (offset + len + mask) & ~mask;
+
+        /* We only support the FALLOC_FL_KEEP_SIZE mode */
+        if (mode & ~FALLOC_FL_KEEP_SIZE)
+                return -EOPNOTSUPP;
+
+        /*
+         * wait for ordered IO before we have any locks.  We'll loop again
+         * below with the locks held.
+         */
+        btrfs_wait_ordered_range(inode, alloc_start, alloc_end - alloc_start);
+
+        mutex_lock(&inode->i_mutex);
+        ret = inode_newsize_ok(inode, alloc_end);
+        if (ret)
+                goto out;
+
+        if (alloc_start > inode->i_size) {
+                ret = btrfs_cont_expand(inode, alloc_start);
+                if (ret)
+                        goto out;
+        }
+
+        ret = btrfs_check_data_free_space(inode, alloc_end - alloc_start);
+        if (ret)
+                goto out;
+
+        locked_end = alloc_end - 1;
+        while (1) {
+                struct btrfs_ordered_extent *ordered;
+
+                /* the extent lock is ordered inside the running
+                 * transaction
+                 */
+                lock_extent_bits(&BTRFS_I(inode)->io_tree, alloc_start,
+                                 locked_end, 0, &cached_state, GFP_NOFS);
+                ordered = btrfs_lookup_first_ordered_extent(inode,
+                                                            alloc_end - 1);
+                if (ordered &&
+                    ordered->file_offset + ordered->len > alloc_start &&
+                    ordered->file_offset < alloc_end) {
+                        btrfs_put_ordered_extent(ordered);
+                        unlock_extent_cached(&BTRFS_I(inode)->io_tree,
+                                             alloc_start, locked_end,
+                                             &cached_state, GFP_NOFS);
+                        /*
+                         * we can't wait on the range with the transaction
+                         * running or with the extent lock held
+                         */
+                        btrfs_wait_ordered_range(inode, alloc_start,
+                                                 alloc_end - alloc_start);
+                } else {
+                        if (ordered)
+                                btrfs_put_ordered_extent(ordered);
+                        break;
+                }
+        }
+
+        cur_offset = alloc_start;
+        while (1) {
+                em = btrfs_get_extent(inode, NULL, 0, cur_offset,
+                                      alloc_end - cur_offset, 0);
+                BUG_ON(IS_ERR(em) || !em);
+                last_byte = min(extent_map_end(em), alloc_end);
+                last_byte = (last_byte + mask) & ~mask;
+                if (em->block_start == EXTENT_MAP_HOLE ||
+                    (cur_offset >= inode->i_size &&
+                     !test_bit(EXTENT_FLAG_PREALLOC, &em->flags))) {
+                        ret = btrfs_prealloc_file_range(inode, mode, cur_offset,
+                                                        last_byte - cur_offset,
+                                                        1 << inode->i_blkbits,
+                                                        offset + len,
+                                                        &alloc_hint);
+                        if (ret < 0) {
+                                free_extent_map(em);
+                                break;
+                        }
+                }
+                free_extent_map(em);
+
+                cur_offset = last_byte;
+                if (cur_offset >= alloc_end) {
+                        ret = 0;
+                        break;
+                }
+        }
+        unlock_extent_cached(&BTRFS_I(inode)->io_tree, alloc_start, locked_end,
+                             &cached_state, GFP_NOFS);
+
+        btrfs_free_reserved_data_space(inode, alloc_end - alloc_start);
+out:
+        mutex_unlock(&inode->i_mutex);
+        return ret;
+}
+
 const struct file_operations btrfs_file_operations = {
         .llseek         = generic_file_llseek,
         .read           = do_sync_read,
@@ -1248,6 +1360,7 @@ const struct file_operations btrfs_file_operations = {
         .open           = generic_file_open,
         .release        = btrfs_release_file,
         .fsync          = btrfs_sync_file,
+        .fallocate      = btrfs_fallocate,
         .unlocked_ioctl = btrfs_ioctl,
 #ifdef CONFIG_COMPAT
         .compat_ioctl   = btrfs_ioctl,