/**
* 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: cl_isize_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 = vvp_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) {
/* 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);
loff_t cur_index = start >> PAGE_SHIFT;
loff_t size_index = (size - 1) >> PAGE_SHIFT;
if ((size == 0 && cur_index != 0) ||
size_index < cur_index)
*exceed = 1;
}
int cl_glimpse_size0(struct inode *inode, int agl)
{
/*
* We don't need ast_flags argument to cl_glimpse_size(), because
* osc_lock_enqueue() takes care of the possible deadlock that said
* argument was introduced to avoid.
*/
/*
* XXX but note that ll_file_seek() passes LDLM_FL_BLOCK_NOWAIT to
* cl_glimpse_size(), which doesn't make sense: glimpse locks are not
* blocking anyway.
*/
struct lu_env *env = NULL;
struct cl_io *io = NULL;
__u16 refcheck;
int retried = 0;
int result;
ENTRY;
result = cl_io_get(inode, &env, &io, &refcheck);
if (result <= 0)
RETURN(result);
do {
io->ci_ndelay_tried = retried++;
io->ci_ndelay = io->ci_verify_layout = 1;
result = cl_io_init(env, io, CIT_GLIMPSE, io->ci_obj);
if (result > 0) {
/*
* nothing to do for this io. This currently happens
* when stripe sub-object's are not yet created.
*/
result = io->ci_result;
} else if (result == 0) {
result = cl_glimpse_lock(env, io, inode, io->ci_obj,
agl);
if (!agl && result == -EWOULDBLOCK)
io->ci_need_restart = 1;
}
OBD_FAIL_TIMEOUT(OBD_FAIL_GLIMPSE_DELAY, 2);
cl_io_fini(env, io);
} while (unlikely(io->ci_need_restart));
cl_env_put(env, &refcheck);
RETURN(result);
}