Cursor in readdir

Hi Miklos,

Sorry for disturb you. I'm confused with *cursor* in struct ovl_dir_file. I know this struct ovl_cache_entry *cursor* is presented to indicate current pos when performing readdir at a MERGE type directory.

Why this additional entry is needed? Can't we use a pointer to record which entry is read or is ready for reading? After finish reading lower and upper directories, entries in struct ovl_dir_cache is stabilized. Changing of directories will cause the later .readdir() to create a new ovl_dir_cache but the old cache will not be released until all the holders of it call .release().

So I think a pointer points to an entry in the entry list of ovl_dir_cache is enough to each process sharing the access of the same cache. We don't need to keep and move an special entry, *cursor*. That's my thought.

Quoted 15 lines · hujianyang

Hi Miklos,

Sorry for disturb you. I'm confused with *cursor* in struct ovl_dir_file. I know this struct ovl_cache_entry *cursor* is presented to indicate current pos when performing readdir at a MERGE type directory.

Why this additional entry is needed? Can't we use a pointer to record which entry is read or is ready for reading? After finish reading lower and upper directories, entries in struct ovl_dir_cache is stabilized. Changing of directories will cause the later .readdir() to create a new ovl_dir_cache but the old cache will not be released until all the holders of it call .release().

Quoted 4 lines

So I think a pointer points to an entry in the entry list of ovl_dir_cache is enough to each process sharing the access of the same cache. We don't need to keep and move an special entry, *cursor*. That's my thought.

Cursors are safe against removal of current entry. However, we don't
do that here, AFAICS, so I think you are correct in that the cursor is not actually needed here.

On 2014/12/1 23:26, Miklos Szeredi wrote:

Do you think it's valuable to discard the using of *cursor* and use a pointer instead? Or maybe we will enable some remove operations for ovl_dir_cache in the future so we should keep this mechanism.

What's your opinion? I'd like to change this part and see if the usage of a pointer could speed up .readdir() on a merged directory.