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[13.113.80.70]) by smtp.gmail.com with ESMTPSA id y23-20020a63ce17000000b004123c6a084dsm5422582pgf.22.2022.07.06.02.15.26 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 06 Jul 2022 02:15:28 -0700 (PDT) From: Zhang Boyang To: linux-block@vger.kernel.org Cc: Jens Axboe , Christoph Hellwig , linux-kernel@vger.kernel.org, Zhang Boyang Subject: [PATCH] loop: introduce LO_FLAGS_NODEALLOC Date: Wed, 6 Jul 2022 17:14:55 +0800 Message-Id: <20220706091455.35063-1-zhangboyang.id@gmail.com> X-Mailer: git-send-email 2.30.2 MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" Previously, for file-backed loop devices, REQ_OP_DISCARD and REQ_OP_WRITE_ZEROES (without REQ_NOUNMAP) are implemented using fallocate(FALLOC_FL_PUNCH_HOLE), which will cause the underlying file to be sparse and disk space freed. The users have no choice to prevent this this from happening. This patch introduces LO_FLAGS_NODEALLOC. With this flag set, REQ_OP_DISCARD and REQ_OP_WRITE_ZEROES are forced to use fallocate(FALLOC_FL_ZERO_RANGE). The disk space of underlying file is kept allocated. This is useful if users, for example, want to use a preallocated file as the backing file. Signed-off-by: Zhang Boyang --- drivers/block/loop.c | 17 +++++++++++++++-- include/uapi/linux/loop.h | 15 +++++++++++---- 2 files changed, 26 insertions(+), 6 deletions(-) diff --git a/drivers/block/loop.c b/drivers/block/loop.c index 084f9b8a0ba3..a52ef0787202 100644 --- a/drivers/block/loop.c +++ b/drivers/block/loop.c @@ -483,11 +483,15 @@ static int do_req_filebacked(struct loop_device *lo, = struct request *rq) * write zeroes the range. Otherwise, punch them out. */ return lo_fallocate(lo, rq, pos, - (rq->cmd_flags & REQ_NOUNMAP) ? + ((rq->cmd_flags & REQ_NOUNMAP) || + (lo->lo_flags & LO_FLAGS_NODEALLOC)) ? FALLOC_FL_ZERO_RANGE : FALLOC_FL_PUNCH_HOLE); case REQ_OP_DISCARD: - return lo_fallocate(lo, rq, pos, FALLOC_FL_PUNCH_HOLE); + return lo_fallocate(lo, rq, pos, + (lo->lo_flags & LO_FLAGS_NODEALLOC) ? + FALLOC_FL_ZERO_RANGE : + FALLOC_FL_PUNCH_HOLE); case REQ_OP_WRITE: if (cmd->use_aio) return lo_rw_aio(lo, cmd, pos, WRITE); @@ -719,12 +723,20 @@ static ssize_t loop_attr_dio_show(struct loop_device = *lo, char *buf) return sysfs_emit(buf, "%s\n", dio ? "1" : "0"); } =20 +static ssize_t loop_attr_nodealloc_show(struct loop_device *lo, char *buf) +{ + int nodealloc =3D (lo->lo_flags & LO_FLAGS_NODEALLOC); + + return sysfs_emit(buf, "%s\n", nodealloc ? "1" : "0"); +} + LOOP_ATTR_RO(backing_file); LOOP_ATTR_RO(offset); LOOP_ATTR_RO(sizelimit); LOOP_ATTR_RO(autoclear); LOOP_ATTR_RO(partscan); LOOP_ATTR_RO(dio); +LOOP_ATTR_RO(nodealloc); =20 static struct attribute *loop_attrs[] =3D { &loop_attr_backing_file.attr, @@ -733,6 +745,7 @@ static struct attribute *loop_attrs[] =3D { &loop_attr_autoclear.attr, &loop_attr_partscan.attr, &loop_attr_dio.attr, + &loop_attr_nodealloc.attr, NULL, }; =20 diff --git a/include/uapi/linux/loop.h b/include/uapi/linux/loop.h index 6f63527dd2ed..a6afd06ffa07 100644 --- a/include/uapi/linux/loop.h +++ b/include/uapi/linux/loop.h @@ -18,17 +18,24 @@ enum { LO_FLAGS_AUTOCLEAR =3D 4, LO_FLAGS_PARTSCAN =3D 8, LO_FLAGS_DIRECT_IO =3D 16, + LO_FLAGS_NODEALLOC =3D 32, }; =20 /* LO_FLAGS that can be set using LOOP_SET_STATUS(64) */ -#define LOOP_SET_STATUS_SETTABLE_FLAGS (LO_FLAGS_AUTOCLEAR | LO_FLAGS_PART= SCAN) +#define LOOP_SET_STATUS_SETTABLE_FLAGS (LO_FLAGS_AUTOCLEAR \ + | LO_FLAGS_PARTSCAN \ + | LO_FLAGS_NODEALLOC) =20 /* LO_FLAGS that can be cleared using LOOP_SET_STATUS(64) */ -#define LOOP_SET_STATUS_CLEARABLE_FLAGS (LO_FLAGS_AUTOCLEAR) +#define LOOP_SET_STATUS_CLEARABLE_FLAGS (LO_FLAGS_AUTOCLEAR \ + | LO_FLAGS_NODEALLOC) =20 /* LO_FLAGS that can be set using LOOP_CONFIGURE */ -#define LOOP_CONFIGURE_SETTABLE_FLAGS (LO_FLAGS_READ_ONLY | LO_FLAGS_AUTOC= LEAR \ - | LO_FLAGS_PARTSCAN | LO_FLAGS_DIRECT_IO) +#define LOOP_CONFIGURE_SETTABLE_FLAGS (LO_FLAGS_READ_ONLY \ + | LO_FLAGS_AUTOCLEAR \ + | LO_FLAGS_PARTSCAN \ + | LO_FLAGS_DIRECT_IO \ + | LO_FLAGS_NODEALLOC) =20 #include /* for __kernel_old_dev_t */ #include /* for __u64 */ --=20 2.30.2