From: Pavel Begunkov <asml.silence@gmail.com>
To: Lennert Buytenhek <buytenh@wantstofly.org>,
Jens Axboe <axboe@kernel.dk>, Al Viro <viro@zeniv.linux.org.uk>,
linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
io-uring@vger.kernel.org
Cc: David Laight <David.Laight@aculab.com>,
Matthew Wilcox <willy@infradead.org>
Subject: Re: [PATCH v3 2/2] io_uring: add support for IORING_OP_GETDENTS
Date: Fri, 19 Feb 2021 12:10:02 +0000 [thread overview]
Message-ID: <8b675c3d-3d25-aaca-7796-e02bba2da01a@gmail.com> (raw)
In-Reply-To: <9a6fb59b-be85-c36b-3c83-26cff37bcb87@gmail.com>
On 19/02/2021 12:05, Pavel Begunkov wrote:
> On 18/02/2021 12:27, Lennert Buytenhek wrote:
>> IORING_OP_GETDENTS behaves much like getdents64(2) and takes the same
>> arguments, but with a small twist: it takes an additional offset
>> argument, and reading from the specified directory starts at the given
>> offset.
>>
>> For the first IORING_OP_GETDENTS call on a directory, the offset
>> parameter can be set to zero, and for subsequent calls, it can be
>> set to the ->d_off field of the last struct linux_dirent64 returned
>> by the previous IORING_OP_GETDENTS call.
>>
>> Internally, if necessary, IORING_OP_GETDENTS will vfs_llseek() to
>> the right directory position before calling vfs_getdents().
>>
>> IORING_OP_GETDENTS may or may not update the specified directory's
>> file offset, and the file offset should not be relied upon having
>> any particular value during or after an IORING_OP_GETDENTS call.
>>
>> Signed-off-by: Lennert Buytenhek <buytenh@wantstofly.org>
>> ---
>> fs/io_uring.c | 73 +++++++++++++++++++++++++++++++++++
>> include/uapi/linux/io_uring.h | 1 +
>> 2 files changed, 74 insertions(+)
>>
>> diff --git a/fs/io_uring.c b/fs/io_uring.c
>> index 056bd4c90ade..6853bf48369a 100644
>> --- a/fs/io_uring.c
>> +++ b/fs/io_uring.c
>> @@ -635,6 +635,13 @@ struct io_mkdir {
>> struct filename *filename;
>> };
>>
> [...]
>> +static int io_getdents(struct io_kiocb *req, unsigned int issue_flags)
>> +{
>> + struct io_getdents *getdents = &req->getdents;
>> + bool pos_unlock = false;
>> + int ret = 0;
>> +
>> + /* getdents always requires a blocking context */
>> + if (issue_flags & IO_URING_F_NONBLOCK)
>> + return -EAGAIN;
>> +
>> + /* for vfs_llseek and to serialize ->iterate_shared() on this file */
>> + if (file_count(req->file) > 1) {
>
> Looks racy, is it safe? E.g. can be concurrently dupped and used, or just
> several similar IORING_OP_GETDENTS requests.
>
>> + pos_unlock = true;
>> + mutex_lock(&req->file->f_pos_lock);
>> + }
>> +
>> + if (req->file->f_pos != getdents->pos) {
>> + loff_t res = vfs_llseek(req->file, getdents->pos, SEEK_SET);
>
> I may be missing the previous discussions, but can this ever become
> stateless, like passing an offset? Including readdir.c and beyond.
I mean without those seeks. An emulation would look like rewinding
pos back after vfs_getdents, though might be awful on performance.
>
>> + if (res < 0)
>> + ret = res;
>> + }
>> +
>> + if (ret == 0) {
>> + ret = vfs_getdents(req->file, getdents->dirent,
>> + getdents->count);
>> + }
>> +
>> + if (pos_unlock)
>> + mutex_unlock(&req->file->f_pos_lock);
>> +
>> + if (ret < 0) {
>> + if (ret == -ERESTARTSYS)
>> + ret = -EINTR;
>> + req_set_fail_links(req);
>> + }
>> + io_req_complete(req, ret);
>> + return 0;
>> +}
> [...]
>
--
Pavel Begunkov
next prev parent reply other threads:[~2021-02-19 12:15 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-18 12:26 [PATCH v3 0/2] io_uring: add support for IORING_OP_GETDENTS Lennert Buytenhek
2021-02-18 12:27 ` [PATCH v3 1/2] readdir: split the core of getdents64(2) out into vfs_getdents() Lennert Buytenhek
2021-02-18 12:27 ` [PATCH v3 2/2] io_uring: add support for IORING_OP_GETDENTS Lennert Buytenhek
2021-02-19 12:05 ` Pavel Begunkov
2021-02-19 12:10 ` Pavel Begunkov [this message]
2021-02-19 18:06 ` Lennert Buytenhek
2021-02-19 12:34 ` Matthew Wilcox
2021-02-19 18:07 ` Lennert Buytenhek
2021-02-19 18:59 ` Lennert Buytenhek
2021-02-20 17:44 ` [PATCH v3 0/2] " David Laight
2021-02-20 18:29 ` Jens Axboe
2021-02-21 19:38 ` David Laight
2021-02-21 21:12 ` Jens Axboe
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