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[70.77.216.213]) by smtp.gmail.com with ESMTPSA id s15sm39437778pgq.4.2019.12.27.21.49.23 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 27 Dec 2019 21:49:24 -0800 (PST) From: Andreas Dilger Message-Id: Content-Type: multipart/signed; boundary="Apple-Mail=_421161AC-7AEB-4F46-B74F-685F54147CC1"; protocol="application/pgp-signature"; micalg=pgp-sha256 Mime-Version: 1.0 (Mac OS X Mail 10.3 \(3273\)) Subject: Re: [PATCH v3 6/6] ovl: add ovl_fadvise() Date: Fri, 27 Dec 2019 22:49:22 -0700 In-Reply-To: <1535374564-8257-7-git-send-email-amir73il@gmail.com> Cc: Miklos Szeredi , Al Viro , Dave Chinner , linux-unionfs@vger.kernel.org, linux-fsdevel@vger.kernel.org To: Amir Goldstein References: <1535374564-8257-1-git-send-email-amir73il@gmail.com> <1535374564-8257-7-git-send-email-amir73il@gmail.com> X-Mailer: Apple Mail (2.3273) Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org --Apple-Mail=_421161AC-7AEB-4F46-B74F-685F54147CC1 Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset=us-ascii On Aug 27, 2018, at 6:56 AM, Amir Goldstein wrote: > > Implement stacked fadvise to fix syscalls readahead(2) and fadvise64(2) > on an overlayfs file. I was just looking into the existence of the "new" fadvise() method in the VFS being able to communicate application hints directly to the filesystem to see if it could be used to address the word size issue in https://bugzilla.kernel.org/show_bug.cgi?id=205957 without adding a new syscall, and came across this patch and the 4/6 patch that adds the vfs_fadvise() function itself (copied below for clarity). It seems to me that this implementation is broken? Only vfs_fadvise() is called from the fadvise64() syscall, and it will call f_op->fadvise() if the filesystem provides this method. Only overlayfs provides the .fadvise method today. However, it looks that ovl_fadvise() calls back into vfs_fadvise() again, in a seemingly endless loop? It seems like generic_fadvise() should be EXPORT_SYMBOL() so that any filesystem that implements its own .fadvise method can do its own thing, and then call generic_fadvise() to handle the remaining MM-specific work. Thoughts? > +int vfs_fadvise(struct file *file, loff_t offset, loff_t len, int advice) > +{ > + if (file->f_op->fadvise) > + return file->f_op->fadvise(file, offset, len, advice); > + > + return generic_fadvise(file, offset, len, advice); > +} > +EXPORT_SYMBOL(vfs_fadvise); > > +int ovl_fadvise(struct file *file, loff_t offset, loff_t len, int advice) > +{ > + struct fd real; > + int ret; > + > + ret = ovl_real_fdget(file, &real); > + if (ret) > + return ret; > + > + /* XXX: do we need mounter credentials? */ > + ret = vfs_fadvise(real.file, offset, len, advice); > + > + fdput(real); > + > + return ret; > +} Cheers, Andreas --Apple-Mail=_421161AC-7AEB-4F46-B74F-685F54147CC1 Content-Transfer-Encoding: 7bit Content-Disposition: attachment; filename=signature.asc Content-Type: application/pgp-signature; name=signature.asc Content-Description: Message signed with OpenPGP -----BEGIN PGP SIGNATURE----- Comment: GPGTools - http://gpgtools.org iQIzBAEBCAAdFiEEDb73u6ZejP5ZMprvcqXauRfMH+AFAl4G7OIACgkQcqXauRfM H+CjVxAAhKXjX5m11b4E2eMFMuEYZ5wxLrAnFTwzy3gJBvWmL6OhiqlEPuL/TlDp 9LAofpHJGYG1NV1cD7z+RsXoL6o7Qmek2WcebDreuW4SqWflXUa+WyVaQ2JO6Zed V4aq09Q9Sa3EDFF0BZDzUUvgbLbSnxQ/hrds0P8jeX3yE4d/+KArxFbzYY2sDFHb eo60Qj5gQGgW2K+brp9p+p+Ryt7SEUbEKnkwqcNZ3ulqy+pE9YJuKt7KSs+s/BJg IJysWpg3KY3ZV6g/Uewn0rtJDedHn1C55zHHyTC9wN6FDgC8fiCvsIAs48Srfp/p xHJJDUIVhlZj3fk9f9yE76X9m5H6jLMEOwH5x7m+mmlxuibc8oT+0GfgHrjF2CkW ES5/9E7zXLyxIacHEy68Jfa2nnNxxW5ExX7R37rJmvvT1khAfuEsurld209WU4ZU Jk7WHrryeCRVo+HUjWQvLDYDSAiCMmzHhWpmw7A9yOqGw6gzNeecI0lchZuQCFnD O79AeQRSJoxw5RvJ2zQY9P58tZwTrbhvYuaePX4vCKii2NycDKQaUOtrljGfZAT0 hGyJQVo0cDupp5Wxcojl9Q3+9qcJHfEc5S5Ww5ipg9D0LmlknRaSBLMl8ezA0bq0 G9uihpfQj2igPXtN/EjbVy6GJpOYeDBh/JMh36zC2SfoZi9Xm+k= =MTn5 -----END PGP SIGNATURE----- --Apple-Mail=_421161AC-7AEB-4F46-B74F-685F54147CC1--