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bh=HwFjO0iC2QO9Q3sXzEwRi6E1KuOJkKul953Lgsb1neM=; b=dxZiQMNzIbFkpcgBv1x2syXhirjiE/E+djdNSO21QlfDstmg7TF5wec9fEONGvWiwWvpS0 RzUA2A2cUs3sOxZIi/WPqE4KjxpkVvefmwhMAfNfMCkCkZSFpL0u7keGpEvZquCUDfzEP4 tlZiHD9IobyhJY3IxU23s32LaveE4Kk= X-MC-Unique: vIvnZyeOMR2XIoRcmO0IMw-1 From: Maxim Levitsky To: qemu-devel@nongnu.org Subject: [PATCH 2/5] file-posix: add sg_get_max_segments that actually works with sg Date: Wed, 4 Nov 2020 19:32:14 +0200 Message-Id: <20201104173217.417538-3-mlevitsk@redhat.com> In-Reply-To: <20201104173217.417538-1-mlevitsk@redhat.com> References: <20201104173217.417538-1-mlevitsk@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=mlevitsk@redhat.com 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; 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charset="utf-8" From: Tom Yan sg devices have different major/minor than their corresponding block devices. Using sysfs to get max segments never really worked for them. Fortunately the sg driver provides an ioctl to get sg_tablesize, which is apparently equivalent to max segments. Signed-off-by: Tom Yan Signed-off-by: Maxim Levitsky --- block/file-posix.c | 22 +++++++++++++++++++++- 1 file changed, 21 insertions(+), 1 deletion(-) diff --git a/block/file-posix.c b/block/file-posix.c index 6581f41b2b..c4df757504 100644 --- a/block/file-posix.c +++ b/block/file-posix.c @@ -1181,6 +1181,26 @@ static int sg_get_max_transfer_length(int fd) #endif } =20 +static int sg_get_max_segments(int fd) +{ + /* + * /dev/sg* character devices report 'max_segments' via + * SG_GET_SG_TABLESIZE ioctl + */ + +#ifdef SG_GET_SG_TABLESIZE + long max_segments =3D 0; + + if (ioctl(fd, SG_GET_SG_TABLESIZE, &max_segments) =3D=3D 0) { + return max_segments; + } else { + return -errno; + } +#else + return -ENOSYS; +#endif +} + static int get_max_transfer_length(int fd) { #if defined(BLKSECTGET) && defined(BLKSSZGET) @@ -1269,7 +1289,7 @@ static void hdev_refresh_limits(BlockDriverState *bs,= Error **errp) bs->bl.max_transfer =3D pow2floor(ret); } =20 - ret =3D get_max_segments(s->fd); + ret =3D bs->sg ? sg_get_max_segments(s->fd) : get_max_segments(s->fd); if (ret > 0) { bs->bl.max_transfer =3D MIN_NON_ZERO(bs->bl.max_transfer, ret * qemu_real_host_page_size); --=20 2.26.2