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Tue, 10 Dec 2024 15:19:51 +0800 Message-ID: <568698a0-c2f2-45d8-9d8b-e22e942fa422@huawei.com> Date: Tue, 10 Dec 2024 15:19:51 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird From: Kefeng Wang Subject: Re: [PATCH -next] ovl: respect underlying filesystem's get_unmapped_area() To: Amir Goldstein CC: Lorenzo Stoakes , Jinjiang Tu , , , , , , , , , Matthew Wilcox References: <20241205143038.3260233-1-tujinjiang@huawei.com> <69b72e3d-b101-4641-9ce5-51346c93a98d@lucifer.local> <041dcc1a-0630-27b9-661b-8c64a3775426@huawei.com> Content-Language: en-US In-Reply-To: Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 8bit X-Originating-IP: [10.174.177.243] X-ClientProxiedBy: dggems704-chm.china.huawei.com (10.3.19.181) To dggpemf100008.china.huawei.com (7.185.36.138) X-Rspamd-Queue-Id: 7893C10000E X-Stat-Signature: r9x6hmw647ijhscncspmfkothnbiisin X-Rspam-User: X-Rspamd-Server: rspam09 X-HE-Tag: 1733815172-875269 X-HE-Meta: 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 dKIGyNiu aMgNzZBJ571cTTjnuvCc064/e8mgTkKnh6PqH0LlfIpEwc3OM7rpctpApGb/6Y5hQ4fvjAv0c557jsiO1psf8HtOFB8e76XI1ExsSMinjwdyPkpSxczVGDzTnrAd6N8Jv2ox+l4+sTohTURXqI90xfLvmddnGBIAE0J5osMgHLkHkWhmbOurE2Bug1Rwt7lDZR6zMm2VHcxFnpN+ZXmadQiU2NCcQPBXQqnKYbw/g1Z9BfwQrlvmOQoGHzWpRlGJa/jYtM4LMI1pDMPE= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 2024/12/6 20:58, Amir Goldstein wrote: > On Fri, Dec 6, 2024 at 11:45 AM Kefeng Wang wrote: >> ... >> >> So maybe use mm_get_unmapped_area() instead of __get_unmapped_area(), >> something like below, >> >> +static unsigned long ovl_get_unmapped_area(struct file *file, >> + unsigned long addr, unsigned long len, unsigned long pgoff, >> + unsigned long flags) >> +{ >> + struct file *realfile; >> + const struct cred *old_cred; >> + >> + realfile = ovl_real_file(file); >> + if (IS_ERR(realfile)) >> + return PTR_ERR(realfile); >> + >> + if (realfile->f_op->get_unmapped_area) { >> + unsigned long ret; >> + >> + old_cred = ovl_override_creds(file_inode(file)->i_sb); >> + ret = realfile->f_op->get_unmapped_area(realfile, addr, len, >> + pgoff, flags); >> + ovl_revert_creds(old_cred); >> + >> + if (ret) >> + return ret; >> + } >> + >> + return mm_get_unmapped_area(current->mm, file, addr, len, pgoff, >> flags); >> +} >> >> Correct me If I'm wrong. >> > > You just need to be aware of the fact that between ovl_get_unmapped_area() > and ovl_mmap(), ovl_real_file(file) could change from the lower file, to the > upper file due to another operation that initiated copy-up. Not sure about this part(I have very little knowledge of ovl), do you mean that we could not use ovl_real_file()? The ovl_mmap() using realfile = file->private_data, we may use similar way in ovl_get_unmapped_area(). but I may have misunderstood. Thanks.