Amir Goldstein <amir73il@xxxxxxxxx> writes:
> On Fri, Jan 26, 2024 at 1:57 AM Vinicius Costa Gomes
> <vinicius.gomes@xxxxxxxxx> wrote:
>>
>> For backing file operations, users are expected to pass credentials
>> that will outlive the backing file common operations.
>>
>> Use the specialized guard statements to override/revert the
>> credentials.
>>
>
> As I wrote before, I prefer to see this patch gets reviewed and merged
> before the overlayfs large patch, so please reorder the series.
>
Sure. Will do.
>> Signed-off-by: Vinicius Costa Gomes <vinicius.gomes@xxxxxxxxx>
>> ---
>> fs/backing-file.c | 124 ++++++++++++++++++++++------------------------
>> 1 file changed, 60 insertions(+), 64 deletions(-)
>>
>> diff --git a/fs/backing-file.c b/fs/backing-file.c
>> index a681f38d84d8..9874f09f860f 100644
>> --- a/fs/backing-file.c
>> +++ b/fs/backing-file.c
>> @@ -140,7 +140,7 @@ ssize_t backing_file_read_iter(struct file *file, struct iov_iter *iter,
>> struct backing_file_ctx *ctx)
>> {
>> struct backing_aio *aio = NULL;
>> - const struct cred *old_cred;
>> + const struct cred *old_cred = ctx->cred;
>> ssize_t ret;
>>
>> if (WARN_ON_ONCE(!(file->f_mode & FMODE_BACKING)))
>> @@ -153,29 +153,28 @@ ssize_t backing_file_read_iter(struct file *file, struct iov_iter *iter,
>> !(file->f_mode & FMODE_CAN_ODIRECT))
>> return -EINVAL;
>>
>> - old_cred = override_creds(ctx->cred);
>> - if (is_sync_kiocb(iocb)) {
>> - rwf_t rwf = iocb_to_rw_flags(flags);
>> + scoped_guard(cred, old_cred) {
>
> This reads very strage.
>
> Also, I see that e.g. scoped_guard(spinlock_irqsave, ... hides the local var
> used for save/restore of flags inside the macro.
>
> Perhaps you use the same technique for scoped_guard(cred, ..
> loose the local old_cred variable in all those functions and then the
> code will read:
>
> scoped_guard(cred, ctx->cred) {
>
> which is nicer IMO.
Most likely using DEFINE_LOCK_GUARD_1() would allow us to use the nicer version.
>
>> + if (is_sync_kiocb(iocb)) {
>> + rwf_t rwf = iocb_to_rw_flags(flags);
>>
>> - ret = vfs_iter_read(file, iter, &iocb->ki_pos, rwf);
>> - } else {
>> - ret = -ENOMEM;
>> - aio = kmem_cache_zalloc(backing_aio_cachep, GFP_KERNEL);
>> - if (!aio)
>> - goto out;
>> + ret = vfs_iter_read(file, iter, &iocb->ki_pos, rwf);
>> + } else {
>> + ret = -ENOMEM;
>> + aio = kmem_cache_zalloc(backing_aio_cachep, GFP_KERNEL);
>> + if (!aio)
>> + goto out;
>>
>> - aio->orig_iocb = iocb;
>> - kiocb_clone(&aio->iocb, iocb, get_file(file));
>> - aio->iocb.ki_complete = backing_aio_rw_complete;
>> - refcount_set(&aio->ref, 2);
>> - ret = vfs_iocb_iter_read(file, &aio->iocb, iter);
>> - backing_aio_put(aio);
>> - if (ret != -EIOCBQUEUED)
>> - backing_aio_cleanup(aio, ret);
>> + aio->orig_iocb = iocb;
>> + kiocb_clone(&aio->iocb, iocb, get_file(file));
>> + aio->iocb.ki_complete = backing_aio_rw_complete;
>> + refcount_set(&aio->ref, 2);
>> + ret = vfs_iocb_iter_read(file, &aio->iocb, iter);
>> + backing_aio_put(aio);
>> + if (ret != -EIOCBQUEUED)
>> + backing_aio_cleanup(aio, ret);
>> + }
>
> if possible, I would rather avoid all this churn in functions that mostly
> do work with the new cred, so either use guard(cred, ) directly or split a
> helper that uses guard(cred, ) form the rest.
>
Yeah, I think what happened is that I tried to keep the scope of the
guard to be as close as possible to override/revert (as you said), and
that caused the churn.
Probably using guard() more will reduce these confusing code changes. I
am going to try that.
> Thanks,
> Amir.
Cheers,
--
Vinicius
