+static void vvp_object_size_lock(struct cl_object *obj)
+{
+ struct inode *inode = vvp_object_inode(obj);
+
+ ll_inode_size_lock(inode);
+ cl_object_attr_lock(obj);
+}
+
+static void vvp_object_size_unlock(struct cl_object *obj)
+{
+ struct inode *inode = vvp_object_inode(obj);
+
+ cl_object_attr_unlock(obj);
+ ll_inode_size_unlock(inode);
+}
+
+/**
+ * Helper function that if necessary adjusts file size (inode->i_size), when
+ * position at the offset \a pos is accessed. File size can be arbitrary stale
+ * on a Lustre client, but client at least knows KMS. If accessed area is
+ * inside [0, KMS], set file size to KMS, otherwise glimpse file size.
+ *
+ * Locking: i_size_lock is used to serialize changes to inode size and to
+ * protect consistency between inode size and cl_object
+ * attributes. cl_object_size_lock() protects consistency between cl_attr's of
+ * top-object and sub-objects.
+ */
+static int vvp_prep_size(const struct lu_env *env, struct cl_object *obj,
+ struct cl_io *io, loff_t start, size_t count,
+ int *exceed)
+{
+ struct cl_attr *attr = ccc_env_thread_attr(env);
+ struct inode *inode = vvp_object_inode(obj);
+ loff_t pos = start + count - 1;
+ loff_t kms;
+ int result;
+
+ /*
+ * Consistency guarantees: following possibilities exist for the
+ * relation between region being accessed and real file size at this
+ * moment:
+ *
+ * (A): the region is completely inside of the file;
+ *
+ * (B-x): x bytes of region are inside of the file, the rest is
+ * outside;
+ *
+ * (C): the region is completely outside of the file.
+ *
+ * This classification is stable under DLM lock already acquired by
+ * the caller, because to change the class, other client has to take
+ * DLM lock conflicting with our lock. Also, any updates to ->i_size
+ * by other threads on this client are serialized by
+ * ll_inode_size_lock(). This guarantees that short reads are handled
+ * correctly in the face of concurrent writes and truncates.
+ */
+ vvp_object_size_lock(obj);
+ result = cl_object_attr_get(env, obj, attr);
+ if (result == 0) {
+ kms = attr->cat_kms;
+ if (pos > kms) {
+ /*
+ * A glimpse is necessary to determine whether we
+ * return a short read (B) or some zeroes at the end
+ * of the buffer (C)
+ */
+ vvp_object_size_unlock(obj);
+ result = cl_glimpse_lock(env, io, inode, obj, 0);
+ if (result == 0 && exceed != NULL) {
+ /* If objective page index exceed end-of-file
+ * page index, return directly. Do not expect
+ * kernel will check such case correctly.
+ * linux-2.6.18-128.1.1 miss to do that.
+ * --bug 17336 */
+ loff_t size = i_size_read(inode);
+ unsigned long cur_index = start >>
+ PAGE_CACHE_SHIFT;
+
+ if ((size == 0 && cur_index != 0) ||
+ (((size - 1) >> PAGE_CACHE_SHIFT) <
+ cur_index))
+ *exceed = 1;
+ }
+
+ return result;
+ } else {
+ /*
+ * region is within kms and, hence, within real file
+ * size (A). We need to increase i_size to cover the
+ * read region so that generic_file_read() will do its
+ * job, but that doesn't mean the kms size is
+ * _correct_, it is only the _minimum_ size. If
+ * someone does a stat they will get the correct size
+ * which will always be >= the kms value here.
+ * b=11081
+ */
+ if (i_size_read(inode) < kms) {
+ i_size_write(inode, kms);
+ CDEBUG(D_VFSTRACE,
+ DFID" updating i_size "LPU64"\n",
+ PFID(lu_object_fid(&obj->co_lu)),
+ (__u64)i_size_read(inode));
+ }
+ }
+ }
+
+ vvp_object_size_unlock(obj);
+
+ return result;
+}
+
git://git.whamcloud.com / fs / lustre-release.git / blobdiff