return (error);
}
-static int
-zpl_fsync(struct file *filp, struct dentry *dentry, int datasync)
+ZPL_FSYNC_PROTO(zpl_fsync, filp, unused_dentry, datasync)
{
cred_t *cr;
int error;
return (wrote);
}
+/*
+ * It's worth taking a moment to describe how mmap is implemented
+ * for zfs because it differs considerably from other Linux filesystems.
+ * However, this issue is handled the same way under OpenSolaris.
+ *
+ * The issue is that by design zfs bypasses the Linux page cache and
+ * leaves all caching up to the ARC. This has been shown to work
+ * well for the common read(2)/write(2) case. However, mmap(2)
+ * is problem because it relies on being tightly integrated with the
+ * page cache. To handle this we cache mmap'ed files twice, once in
+ * the ARC and a second time in the page cache. The code is careful
+ * to keep both copies synchronized.
+ *
+ * When a file with an mmap'ed region is written to using write(2)
+ * both the data in the ARC and existing pages in the page cache
+ * are updated. For a read(2) data will be read first from the page
+ * cache then the ARC if needed. Neither a write(2) or read(2) will
+ * will ever result in new pages being added to the page cache.
+ *
+ * New pages are added to the page cache only via .readpage() which
+ * is called when the vfs needs to read a page off disk to back the
+ * virtual memory region. These pages may be modified without
+ * notifying the ARC and will be written out periodically via
+ * .writepage(). This will occur due to either a sync or the usual
+ * page aging behavior. Note because a read(2) of a mmap'ed file
+ * will always check the page cache first even when the ARC is out
+ * of date correct data will still be returned.
+ *
+ * While this implementation ensures correct behavior it does have
+ * have some drawbacks. The most obvious of which is that it
+ * increases the required memory footprint when access mmap'ed
+ * files. It also adds additional complexity to the code keeping
+ * both caches synchronized.
+ *
+ * Longer term it may be possible to cleanly resolve this wart by
+ * mapping page cache pages directly on to the ARC buffers. The
+ * Linux address space operations are flexible enough to allow
+ * selection of which pages back a particular index. The trick
+ * would be working out the details of which subsystem is in
+ * charge, the ARC, the page cache, or both. It may also prove
+ * helpful to move the ARC buffers to a scatter-gather lists
+ * rather than a vmalloc'ed region.
+ */
+static int
+zpl_mmap(struct file *filp, struct vm_area_struct *vma)
+{
+ znode_t *zp = ITOZ(filp->f_mapping->host);
+ int error;
+
+ error = generic_file_mmap(filp, vma);
+ if (error)
+ return (error);
+
+ mutex_enter(&zp->z_lock);
+ zp->z_is_mapped = 1;
+ mutex_exit(&zp->z_lock);
+
+ return (error);
+}
+
+/*
+ * Populate a page with data for the Linux page cache. This function is
+ * only used to support mmap(2). There will be an identical copy of the
+ * data in the ARC which is kept up to date via .write() and .writepage().
+ *
+ * Current this function relies on zpl_read_common() and the O_DIRECT
+ * flag to read in a page. This works but the more correct way is to
+ * update zfs_fillpage() to be Linux friendly and use that interface.
+ */
+static int
+zpl_readpage(struct file *filp, struct page *pp)
+{
+ struct inode *ip;
+ loff_t off, i_size;
+ size_t len, wrote;
+ cred_t *cr;
+ void *pb;
+ int error = 0;
+
+ ASSERT(PageLocked(pp));
+ ip = pp->mapping->host;
+ off = page_offset(pp);
+ i_size = i_size_read(ip);
+ ASSERT3S(off, <, i_size);
+
+ cr = (cred_t *)get_current_cred();
+ len = MIN(PAGE_CACHE_SIZE, i_size - off);
+
+ pb = kmap(pp);
+
+ /* O_DIRECT is passed to bypass the page cache and avoid deadlock. */
+ wrote = zpl_read_common(ip, pb, len, off, UIO_SYSSPACE, O_DIRECT, cr);
+ if (wrote != len)
+ error = -EIO;
+
+ if (!error && (len < PAGE_CACHE_SIZE))
+ memset(pb + len, 0, PAGE_CACHE_SIZE - len);
+
+ kunmap(pp);
+ put_cred(cr);
+
+ if (error) {
+ SetPageError(pp);
+ ClearPageUptodate(pp);
+ } else {
+ ClearPageError(pp);
+ SetPageUptodate(pp);
+ flush_dcache_page(pp);
+ }
+
+ unlock_page(pp);
+
+ return (error);
+}
+
+/*
+ * Write out dirty pages to the ARC, this function is only required to
+ * support mmap(2). Mapped pages may be dirtied by memory operations
+ * which never call .write(). These dirty pages are kept in sync with
+ * the ARC buffers via this hook.
+ *
+ * Currently this function relies on zpl_write_common() and the O_DIRECT
+ * flag to push out the page. This works but the more correct way is
+ * to update zfs_putapage() to be Linux friendly and use that interface.
+ */
+static int
+zpl_writepage(struct page *pp, struct writeback_control *wbc)
+{
+ struct inode *ip;
+ loff_t off, i_size;
+ size_t len, read;
+ cred_t *cr;
+ void *pb;
+ int error = 0;
+
+ ASSERT(PageLocked(pp));
+ ip = pp->mapping->host;
+ off = page_offset(pp);
+ i_size = i_size_read(ip);
+
+ cr = (cred_t *)get_current_cred();
+ len = MIN(PAGE_CACHE_SIZE, i_size - off);
+
+ pb = kmap(pp);
+
+ /* O_DIRECT is passed to bypass the page cache and avoid deadlock. */
+ read = zpl_write_common(ip, pb, len, off, UIO_SYSSPACE, O_DIRECT, cr);
+ if (read != len)
+ error = -EIO;
+
+ kunmap(pp);
+ put_cred(cr);
+
+ if (error) {
+ SetPageError(pp);
+ ClearPageUptodate(pp);
+ } else {
+ ClearPageError(pp);
+ SetPageUptodate(pp);
+ }
+
+ unlock_page(pp);
+
+ return (error);
+}
+
const struct address_space_operations zpl_address_space_operations = {
-#if 0
.readpage = zpl_readpage,
.writepage = zpl_writepage,
- .direct_IO = zpl_direct_IO,
-#endif
};
const struct file_operations zpl_file_operations = {
.open = generic_file_open,
.llseek = generic_file_llseek,
- .read = zpl_read, /* do_sync_read */
- .write = zpl_write, /* do_sync_write */
+ .read = zpl_read,
+ .write = zpl_write,
.readdir = zpl_readdir,
- .mmap = generic_file_mmap,
+ .mmap = zpl_mmap,
.fsync = zpl_fsync,
- .aio_read = NULL, /* generic_file_aio_read */
- .aio_write = NULL, /* generic_file_aio_write */
};
const struct file_operations zpl_dir_file_operations = {
git://git.camperquake.de / zfs.git / blobdiff