* Support up to 256 loop devices
* Heinz Mauelshagen <mge@sistina.com>, Feb 2002
*
+ * Support for falling back on the write file operation when the address space
+ * operations prepare_write and/or commit_write are not available on the
+ * backing filesystem.
+ * Anton Altaparmakov, 16 Feb 2005
+ *
* Still To Fix:
* - Advisory locking is ignored here.
* - Should use an own CAP_* category instead of CAP_SYS_ADMIN
#include <linux/writeback.h>
#include <linux/buffer_head.h> /* for invalidate_bdev() */
#include <linux/completion.h>
+#include <linux/highmem.h>
+#include <linux/gfp.h>
#include <asm/uaccess.h>
static int xor_init(struct loop_device *lo, const struct loop_info64 *info)
{
- if (info->lo_encrypt_key_size <= 0)
+ if (unlikely(info->lo_encrypt_key_size <= 0))
return -EINVAL;
return 0;
}
loff_t size = get_loop_size(lo, lo->lo_backing_file);
sector_t x = (sector_t)size;
- if ((loff_t)x != size)
+ if (unlikely((loff_t)x != size))
return -EFBIG;
set_capacity(disks[lo->lo_number], x);
struct page *lpage, unsigned loffs,
int size, sector_t rblock)
{
- if (!lo->transfer)
+ if (unlikely(!lo->transfer))
return 0;
return lo->transfer(lo, cmd, rpage, roffs, lpage, loffs, size, rblock);
}
-static int
-do_lo_send(struct loop_device *lo, struct bio_vec *bvec, int bsize, loff_t pos)
+/**
+ * do_lo_send_aops - helper for writing data to a loop device
+ *
+ * This is the fast version for backing filesystems which implement the address
+ * space operations prepare_write and commit_write.
+ */
+static int do_lo_send_aops(struct loop_device *lo, struct bio_vec *bvec,
+ int bsize, loff_t pos, struct page *page)
{
struct file *file = lo->lo_backing_file; /* kudos to NFsckingS */
struct address_space *mapping = file->f_mapping;
struct address_space_operations *aops = mapping->a_ops;
- struct page *page;
pgoff_t index;
- unsigned size, offset, bv_offs;
- int len;
- int ret = 0;
+ unsigned offset, bv_offs;
+ int len, ret = 0;
down(&mapping->host->i_sem);
index = pos >> PAGE_CACHE_SHIFT;
len = bvec->bv_len;
while (len > 0) {
sector_t IV;
+ unsigned size;
int transfer_result;
IV = ((sector_t)index << (PAGE_CACHE_SHIFT - 9))+(offset >> 9);
-
size = PAGE_CACHE_SIZE - offset;
if (size > len)
size = len;
-
page = grab_cache_page(mapping, index);
- if (!page)
+ if (unlikely(!page))
goto fail;
- if (aops->prepare_write(file, page, offset, offset+size))
+ if (unlikely(aops->prepare_write(file, page, offset,
+ offset + size)))
goto unlock;
transfer_result = lo_do_transfer(lo, WRITE, page, offset,
- bvec->bv_page, bv_offs,
- size, IV);
- if (transfer_result) {
+ bvec->bv_page, bv_offs, size, IV);
+ if (unlikely(transfer_result)) {
char *kaddr;
/*
kunmap_atomic(kaddr, KM_USER0);
}
flush_dcache_page(page);
- if (aops->commit_write(file, page, offset, offset+size))
+ if (unlikely(aops->commit_write(file, page, offset,
+ offset + size)))
goto unlock;
- if (transfer_result)
+ if (unlikely(transfer_result))
goto unlock;
bv_offs += size;
len -= size;
unlock_page(page);
page_cache_release(page);
}
- up(&mapping->host->i_sem);
out:
+ up(&mapping->host->i_sem);
return ret;
-
unlock:
unlock_page(page);
page_cache_release(page);
fail:
- up(&mapping->host->i_sem);
ret = -1;
goto out;
}
-static int
-lo_send(struct loop_device *lo, struct bio *bio, int bsize, loff_t pos)
+/**
+ * __do_lo_send_write - helper for writing data to a loop device
+ *
+ * This helper just factors out common code between do_lo_send_direct_write()
+ * and do_lo_send_write().
+ */
+static inline int __do_lo_send_write(struct file *file,
+ u8 __user *buf, const int len, loff_t pos)
{
+ ssize_t bw;
+ mm_segment_t old_fs = get_fs();
+
+ set_fs(get_ds());
+ bw = file->f_op->write(file, buf, len, &pos);
+ set_fs(old_fs);
+ if (likely(bw == len))
+ return 0;
+ printk(KERN_ERR "loop: Write error at byte offset %llu, length %i.\n",
+ (unsigned long long)pos, len);
+ if (bw >= 0)
+ bw = -EIO;
+ return bw;
+}
+
+/**
+ * do_lo_send_direct_write - helper for writing data to a loop device
+ *
+ * This is the fast, non-transforming version for backing filesystems which do
+ * not implement the address space operations prepare_write and commit_write.
+ * It uses the write file operation which should be present on all writeable
+ * filesystems.
+ */
+static int do_lo_send_direct_write(struct loop_device *lo,
+ struct bio_vec *bvec, int bsize, loff_t pos, struct page *page)
+{
+ ssize_t bw = __do_lo_send_write(lo->lo_backing_file,
+ (u8 __user *)kmap(bvec->bv_page) + bvec->bv_offset,
+ bvec->bv_len, pos);
+ kunmap(bvec->bv_page);
+ cond_resched();
+ return bw;
+}
+
+/**
+ * do_lo_send_write - helper for writing data to a loop device
+ *
+ * This is the slow, transforming version for filesystems which do not
+ * implement the address space operations prepare_write and commit_write. It
+ * uses the write file operation which should be present on all writeable
+ * filesystems.
+ *
+ * Using fops->write is slower than using aops->{prepare,commit}_write in the
+ * transforming case because we need to double buffer the data as we cannot do
+ * the transformations in place as we do not have direct access to the
+ * destination pages of the backing file.
+ */
+static int do_lo_send_write(struct loop_device *lo, struct bio_vec *bvec,
+ int bsize, loff_t pos, struct page *page)
+{
+ int ret = lo_do_transfer(lo, WRITE, page, 0, bvec->bv_page,
+ bvec->bv_offset, bvec->bv_len, pos >> 9);
+ if (likely(!ret))
+ return __do_lo_send_write(lo->lo_backing_file,
+ (u8 __user *)page_address(page), bvec->bv_len,
+ pos);
+ printk(KERN_ERR "loop: Transfer error at byte offset %llu, "
+ "length %i.\n", (unsigned long long)pos, bvec->bv_len);
+ if (ret > 0)
+ ret = -EIO;
+ return ret;
+}
+
+static int lo_send(struct loop_device *lo, struct bio *bio, int bsize,
+ loff_t pos)
+{
+ int (*do_lo_send)(struct loop_device *, struct bio_vec *, int, loff_t,
+ struct page *page);
struct bio_vec *bvec;
+ struct page *page = NULL;
int i, ret = 0;
+ do_lo_send = do_lo_send_aops;
+ if (!(lo->lo_flags & LO_FLAGS_USE_AOPS)) {
+ do_lo_send = do_lo_send_direct_write;
+ if (lo->transfer != transfer_none) {
+ page = alloc_page(GFP_NOIO | __GFP_HIGHMEM);
+ if (unlikely(!page))
+ goto fail;
+ kmap(page);
+ do_lo_send = do_lo_send_write;
+ }
+ }
bio_for_each_segment(bvec, bio, i) {
- ret = do_lo_send(lo, bvec, bsize, pos);
+ ret = do_lo_send(lo, bvec, bsize, pos, page);
if (ret < 0)
break;
pos += bvec->bv_len;
}
+ if (page) {
+ kunmap(page);
+ __free_page(page);
+ }
+out:
return ret;
+fail:
+ printk(KERN_ERR "loop: Failed to allocate temporary page for write.\n");
+ ret = -ENOMEM;
+ goto out;
}
struct lo_read_data {
/* the loop device has to be read-only */
error = -EINVAL;
- if (lo->lo_flags != LO_FLAGS_READ_ONLY)
+ if (!(lo->lo_flags & LO_FLAGS_READ_ONLY))
goto out;
error = -EBADF;
*/
if (!file->f_op->sendfile)
goto out_putf;
-
- if (!aops->prepare_write || !aops->commit_write)
+ if (aops->prepare_write && aops->commit_write)
+ lo_flags |= LO_FLAGS_USE_AOPS;
+ if (!(lo_flags & LO_FLAGS_USE_AOPS) && !file->f_op->write)
lo_flags |= LO_FLAGS_READ_ONLY;
lo_blocksize = inode->i_blksize;
EXPORT_SYMBOL(loop_register_transfer);
EXPORT_SYMBOL(loop_unregister_transfer);
-int __init loop_init(void)
+static int __init loop_init(void)
{
int i;
return -ENOMEM;
}
-void loop_exit(void)
+static void loop_exit(void)
{
int i;
git://git.onelab.eu / linux-2.6.git / blobdiff