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bh=rFOMtfrauKOkTwVYHiiz1g6uh4pzmKAKYAHQfuee8aM=; b=eqH6cpvWxPMhorwiYFav7cekIdLE2zNdww250mxhNAYnaLc4Ke0ATXRape4mv+NsOodRZ7 eiSu6B6qqvLlDmFBuZjWZB30naTPF0Geft9wQm1ZjXpVI08omEaa2VYyfmHb+1JunfEDMb lfFVka1P1JNt7wLug7vSOFTPq9GU8/w= X-MC-Unique: u2McWtaOMOyhr9RY6Lo1vA-1 From: Kevin Wolf To: qemu-block@nongnu.org Subject: [PATCH for-5.1 v2 2/2] file-posix: Allow byte-aligned O_DIRECT with NFS Date: Thu, 16 Jul 2020 16:26:01 +0200 Message-Id: <20200716142601.111237-3-kwolf@redhat.com> In-Reply-To: <20200716142601.111237-1-kwolf@redhat.com> References: <20200716142601.111237-1-kwolf@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Transfer-Encoding: quoted-printable Received-SPF: pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; Received-SPF: pass client-ip=207.211.31.120; envelope-from=kwolf@redhat.com; helo=us-smtp-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/07/16 04:25:38 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -40 X-Spam_score: -4.1 X-Spam_bar: ---- X-Spam_report: (-4.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-1, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: kwolf@redhat.com, qemu-devel@nongnu.org, mreitz@redhat.com Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: "Qemu-devel" X-ZohoMail-DKIM: fail (Header signature does not verify) Content-Type: text/plain; charset="utf-8" Since commit a6b257a08e3 ('file-posix: Handle undetectable alignment'), we assume that if we open a file with O_DIRECT and alignment probing returns 1, we just couldn't find out the real alignment requirement because some filesystems make the requirement only for allocated blocks. In this case, a safe default of 4k is used. This is too strict for NFS, which does actually allow byte-aligned requests even with O_DIRECT. Because we can't distinguish both cases with generic code, let's just look at the file system magic and disable s->needs_alignment for NFS. This way, O_DIRECT can still be used on NFS for images that are not aligned to 4k. Signed-off-by: Kevin Wolf Reviewed-by: Eric Blake Reviewed-by: Max Reitz --- block/file-posix.c | 26 +++++++++++++++++++++++++- 1 file changed, 25 insertions(+), 1 deletion(-) diff --git a/block/file-posix.c b/block/file-posix.c index 8067e238cb..ae8190edab 100644 --- a/block/file-posix.c +++ b/block/file-posix.c @@ -62,10 +62,12 @@ #include #include #include +#include #include #include #include #include +#include #include #ifdef __s390__ #include @@ -300,6 +302,28 @@ static int probe_physical_blocksize(int fd, unsigned i= nt *blk_size) #endif } =20 +/* + * Returns true if no alignment restrictions are necessary even for files + * opened with O_DIRECT. + * + * raw_probe_alignment() probes the required alignment and assume that 1 m= eans + * the probing failed, so it falls back to a safe default of 4k. This can = be + * avoided if we know that byte alignment is okay for the file. + */ +static bool dio_byte_aligned(int fd) +{ +#ifdef __linux__ + struct statfs buf; + int ret; + + ret =3D fstatfs(fd, &buf); + if (ret =3D=3D 0 && buf.f_type =3D=3D NFS_SUPER_MAGIC) { + return true; + } +#endif + return false; +} + /* Check if read is allowed with given memory buffer and length. * * This function is used to check O_DIRECT memory buffer and request align= ment. @@ -629,7 +653,7 @@ static int raw_open_common(BlockDriverState *bs, QDict = *options, =20 s->has_discard =3D true; s->has_write_zeroes =3D true; - if ((bs->open_flags & BDRV_O_NOCACHE) !=3D 0) { + if ((bs->open_flags & BDRV_O_NOCACHE) !=3D 0 && !dio_byte_aligned(s->f= d)) { s->needs_alignment =3D true; } =20 --=20 2.25.4