[PATCH v9 08/21] cachefiles: document on-demand read mode
jefflexu at linux.alibaba.com
Fri Apr 22 13:10:28 AEST 2022
Hi David, thanks for polishing the documents. It's a detailed and
meticulous review again. Really thanks for your time :) I will fix all
these in the next version.
On 4/21/22 10:47 PM, David Howells wrote:
> Jeffle Xu <jefflexu at linux.alibaba.com> wrote:
>> +The essential difference between these two modes is that, in original mode,
>> +when a cache miss occurs, the netfs will fetch the data from the remote server
>> +and then write it to the cache file. With on-demand read mode, however,
>> +fetching the data and writing it into the cache is delegated to a user daemon.
> The starting sentence seems off. How about:
> The essential difference between these two modes is seen when a cache miss
> occurs: In the original mode, the netfs will fetch the data from the remote
> server and then write it to the cache file; in on-demand read mode, fetching
> data and writing it into the cache is delegated to a user daemon.
Okay, it sounds better.
>> the devnode ('/dev/cachefiles') to check if
>> +there's a pending request to be processed. A POLLIN event will be returned
>> +when there's a pending request.
>> +The user daemon then reads the devnode to fetch a request and process it
> Reading the devnode doesn't process the request, so I think something like:
> "... and process it accordingly" -> "... that it can then process."
> "... and process it accordingly" -> "... to process."
Yeah the original statement is indeed misleading.
>> Each cache file has a unique object_id, while it
>> +may have multiple anonymous fds. The user daemon may duplicate anonymous fds
>> +from the initial anonymous fd indicated by the @fd field through dup(). Thus
>> +each object_id can be mapped to multiple anonymous fds, while the usr daemon
>> +itself needs to maintain the mapping.
>> +With the given anonymous fd, the user daemon can fetch data and write it to the
>> +cache file in the background, even when kernel has not triggered a cache miss
>> +The user daemon should complete the READ request
> READ request -> OPEN request?
Good catch. Will be fixed.
>> in the READ request. The ioctl is of the form::
>> + ioctl(fd, CACHEFILES_IOC_CREAD, msg_id);
>> + * ``fd`` is one of the anonymous fds associated with the given object_id
>> + in the READ request.
> the given object_id in the READ request -> object_id
>> + * ``msg_id`` must match the msg_id field of the previous READ request.
> By "previous READ request" is this referring to something different to "the
> READ request" you mentioned against the fd parameter?
Actually it is referring to the same thing (the same READ request). I
will change the statement simply to:
``msg_id`` must match the msg_id field of the READ request.
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