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Fri, 19 Feb 2021 04:13:52 -0800 (PST) Subject: Re: [PATCH v3 2/2] io_uring: add support for IORING_OP_GETDENTS From: Pavel Begunkov To: Lennert Buytenhek , Jens Axboe , Al Viro , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, io-uring@vger.kernel.org Cc: David Laight , Matthew Wilcox References: <20210218122640.GA334506@wantstofly.org> <20210218122755.GC334506@wantstofly.org> <9a6fb59b-be85-c36b-3c83-26cff37bcb87@gmail.com> Autocrypt: addr=asml.silence@gmail.com; prefer-encrypt=mutual; keydata= mQINBFmKBOQBEAC76ZFxLAKpDw0bKQ8CEiYJRGn8MHTUhURL02/7n1t0HkKQx2K1fCXClbps bdwSHrhOWdW61pmfMbDYbTj6ZvGRvhoLWfGkzujB2wjNcbNTXIoOzJEGISHaPf6E2IQx1ik9 6uqVkK1OMb7qRvKH0i7HYP4WJzYbEWVyLiAxUj611mC9tgd73oqZ2pLYzGTqF2j6a/obaqha +hXuWTvpDQXqcOZJXIW43atprH03G1tQs7VwR21Q1eq6Yvy2ESLdc38EqCszBfQRMmKy+cfp W3U9Mb1w0L680pXrONcnlDBCN7/sghGeMHjGKfNANjPc+0hzz3rApPxpoE7HC1uRiwC4et83 CKnncH1l7zgeBT9Oa3qEiBlaa1ZCBqrA4dY+z5fWJYjMpwI1SNp37RtF8fKXbKQg+JuUjAa9 Y6oXeyEvDHMyJYMcinl6xCqCBAXPHnHmawkMMgjr3BBRzODmMr+CPVvnYe7BFYfoajzqzq+h EyXSl3aBf0IDPTqSUrhbmjj5OEOYgRW5p+mdYtY1cXeK8copmd+fd/eTkghok5li58AojCba jRjp7zVOLOjDlpxxiKhuFmpV4yWNh5JJaTbwCRSd04sCcDNlJj+TehTr+o1QiORzc2t+N5iJ NbILft19Izdn8U39T5oWiynqa1qCLgbuFtnYx1HlUq/HvAm+kwARAQABtDFQYXZlbCBCZWd1 bmtvdiAoc2lsZW5jZSkgPGFzbWwuc2lsZW5jZUBnbWFpbC5jb20+iQJOBBMBCAA4FiEE+6Ju PTjTbx479o3OWt5b1Glr+6UFAlmKBOQCGwMFCwkIBwIGFQgJCgsCBBYCAwECHgECF4AACgkQ Wt5b1Glr+6WxZA//QueaKHzgdnOikJ7NA/Vq8FmhRlwgtP0+E+w93kL+ZGLzS/cUCIjn2f4Q Mcutj2Neg0CcYPX3b2nJiKr5Vn0rjJ/suiaOa1h1KzyNTOmxnsqE5fmxOf6C6x+NKE18I5Jy xzLQoktbdDVA7JfB1itt6iWSNoOTVcvFyvfe5ggy6FSCcP+m1RlR58XxVLH+qlAvxxOeEr/e aQfUzrs7gqdSd9zQGEZo0jtuBiB7k98t9y0oC9Jz0PJdvaj1NZUgtXG9pEtww3LdeXP/TkFl HBSxVflzeoFaj4UAuy8+uve7ya/ECNCc8kk0VYaEjoVrzJcYdKP583iRhOLlZA6HEmn/+Gh9 4orG67HNiJlbFiW3whxGizWsrtFNLsSP1YrEReYk9j1SoUHHzsu+ZtNfKuHIhK0sU07G1OPN 2rDLlzUWR9Jc22INAkhVHOogOcc5ajMGhgWcBJMLCoi219HlX69LIDu3Y34uIg9QPZIC2jwr 24W0kxmK6avJr7+n4o8m6sOJvhlumSp5TSNhRiKvAHB1I2JB8Q1yZCIPzx+w1ALxuoWiCdwV M/azguU42R17IuBzK0S3hPjXpEi2sK/k4pEPnHVUv9Cu09HCNnd6BRfFGjo8M9kZvw360gC1 reeMdqGjwQ68o9x0R7NBRrtUOh48TDLXCANAg97wjPoy37dQE7e5Ag0EWYoE5AEQAMWS+aBV IJtCjwtfCOV98NamFpDEjBMrCAfLm7wZlmXy5I6o7nzzCxEw06P2rhzp1hIqkaab1kHySU7g dkpjmQ7Jjlrf6KdMP87mC/Hx4+zgVCkTQCKkIxNE76Ff3O9uTvkWCspSh9J0qPYyCaVta2D1 Sq5HZ8WFcap71iVO1f2/FEHKJNz/YTSOS/W7dxJdXl2eoj3gYX2UZNfoaVv8OXKaWslZlgqN jSg9wsTv1K73AnQKt4fFhscN9YFxhtgD/SQuOldE5Ws4UlJoaFX/yCoJL3ky2kC0WFngzwRF Yo6u/KON/o28yyP+alYRMBrN0Dm60FuVSIFafSqXoJTIjSZ6olbEoT0u17Rag8BxnxryMrgR dkccq272MaSS0eOC9K2rtvxzddohRFPcy/8bkX+t2iukTDz75KSTKO+chce62Xxdg62dpkZX xK+HeDCZ7gRNZvAbDETr6XI63hPKi891GeZqvqQVYR8e+V2725w+H1iv3THiB1tx4L2bXZDI DtMKQ5D2RvCHNdPNcZeldEoJwKoA60yg6tuUquvsLvfCwtrmVI2rL2djYxRfGNmFMrUDN1Xq F3xozA91q3iZd9OYi9G+M/OA01husBdcIzj1hu0aL+MGg4Gqk6XwjoSxVd4YT41kTU7Kk+/I 5/Nf+i88ULt6HanBYcY/+Daeo/XFABEBAAGJAjYEGAEIACAWIQT7om49ONNvHjv2jc5a3lvU aWv7pQUCWYoE5AIbDAAKCRBa3lvUaWv7pfmcEACKTRQ28b1y5ztKuLdLr79+T+LwZKHjX++P 4wKjEOECCcB6KCv3hP+J2GCXDOPZvdg/ZYZafqP68Yy8AZqkfa4qPYHmIdpODtRzZSL48kM8 LRzV8Rl7J3ItvzdBRxf4T/Zseu5U6ELiQdCUkPGsJcPIJkgPjO2ROG/ZtYa9DvnShNWPlp+R uPwPccEQPWO/NP4fJl2zwC6byjljZhW5kxYswGMLBwb5cDUZAisIukyAa8Xshdan6C2RZcNs rB3L7vsg/R8UCehxOH0C+NypG2GqjVejNZsc7bgV49EOVltS+GmGyY+moIzxsuLmT93rqyII 5rSbbcTLe6KBYcs24XEoo49Zm9oDA3jYvNpeYD8rDcnNbuZh9kTgBwFN41JHOPv0W2FEEWqe JsCwQdcOQ56rtezdCJUYmRAt3BsfjN3Jn3N6rpodi4Dkdli8HylM5iq4ooeb5VkQ7UZxbCWt UVMKkOCdFhutRmYp0mbv2e87IK4erwNHQRkHUkzbsuym8RVpAZbLzLPIYK/J3RTErL6Z99N2 m3J6pjwSJY/zNwuFPs9zGEnRO4g0BUbwGdbuvDzaq6/3OJLKohr5eLXNU3JkT+3HezydWm3W OPhauth7W0db74Qd49HXK0xe/aPrK+Cp+kU1HRactyNtF8jZQbhMCC8vMGukZtWaAwpjWiiH bA== Message-ID: <8b675c3d-3d25-aaca-7796-e02bba2da01a@gmail.com> Date: Fri, 19 Feb 2021 12:10:02 +0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.3.0 MIME-Version: 1.0 In-Reply-To: <9a6fb59b-be85-c36b-3c83-26cff37bcb87@gmail.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org 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 >> --- >> 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