From: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
To: Paolo Bonzini <pbonzini@redhat.com>, qemu-devel@nongnu.org
Cc: kwolf@redhat.com, qemu-block@nongnu.org
Subject: Re: [PATCH v3 1/7] file-posix: fix max_iov for /dev/sg devices
Date: Mon, 7 Jun 2021 08:39:34 +0300 [thread overview]
Message-ID: <6426cb5d-9b3e-ca6b-35d4-c4cd5488c448@virtuozzo.com> (raw)
In-Reply-To: <20210603133722.218465-2-pbonzini@redhat.com>
03.06.2021 16:37, Paolo Bonzini wrote:
> Even though it was only called for devices that have bs->sg set (which
> must be character devices),
> sg_get_max_segments looked at /sys/dev/block which only works for
> block devices.
>
> On Linux the sg driver has its own way to provide the maximum number of
> iovecs in a scatter/gather list.
>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
> block/file-posix.c | 11 +++++++++++
> 1 file changed, 11 insertions(+)
>
> diff --git a/block/file-posix.c b/block/file-posix.c
> index f37dfc10b3..58db526cc2 100644
> --- a/block/file-posix.c
> +++ b/block/file-posix.c
> @@ -1180,6 +1180,17 @@ static int sg_get_max_segments(int fd)
> goto out;
> }
>
> + if (S_ISCHR(st->st_mode)) {
> + if (ioctl(fd, SG_GET_SG_TABLESIZE, &ret) == 0) {
> + return ret;
So, this is a new most-probable path for char-dev, yes?
Is it better do it at start of the function to avoid extra fstat() ?
> + }
> + return -EIO;
> + }
> +
> + if (!S_ISBLK(st->st_mode)) {
> + return -ENOTSUP;
> + }
> +
> sysfspath = g_strdup_printf("/sys/dev/block/%u:%u/queue/max_segments",
> major(st.st_rdev), minor(st.st_rdev));
> sysfd = open(sysfspath, O_RDONLY);
>
--
Best regards,
Vladimir
next prev parent reply other threads:[~2021-06-07 5:40 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-03 13:37 [PATCH v3 0/7] block: file-posix queue Paolo Bonzini
2021-06-03 13:37 ` [PATCH v3 1/7] file-posix: fix max_iov for /dev/sg devices Paolo Bonzini
2021-06-07 5:39 ` Vladimir Sementsov-Ogievskiy [this message]
2021-06-07 6:16 ` Vladimir Sementsov-Ogievskiy
2021-06-07 7:23 ` Vladimir Sementsov-Ogievskiy
2021-06-15 15:58 ` Max Reitz
2021-06-03 13:37 ` [PATCH v3 2/7] scsi-generic: pass max_segments via max_iov field in BlockLimits Paolo Bonzini
2021-06-15 16:06 ` Max Reitz
2021-06-15 16:20 ` Max Reitz
2021-06-15 17:41 ` Paolo Bonzini
2021-06-03 13:37 ` [PATCH v3 3/7] block: add max_hw_transfer to BlockLimits Paolo Bonzini
2021-06-03 17:33 ` Eric Blake
2021-06-04 7:21 ` Paolo Bonzini
2021-06-15 16:18 ` Max Reitz
2021-06-16 13:18 ` Paolo Bonzini
2021-06-16 13:46 ` Max Reitz
2021-06-17 9:59 ` Paolo Bonzini
2021-06-03 13:37 ` [PATCH v3 4/7] file-posix: try BLKSECTGET on block devices too, do not round to power of 2 Paolo Bonzini
2021-06-15 16:32 ` Max Reitz
2021-06-03 13:37 ` [PATCH v3 5/7] block: feature detection for host block support Paolo Bonzini
2021-06-15 16:40 ` Max Reitz
2021-06-03 13:37 ` [PATCH v3 6/7] block: check for sys/disk.h Paolo Bonzini
2021-06-15 16:42 ` Max Reitz
2021-06-03 13:37 ` [PATCH v3 7/7] block: detect DKIOCGETBLOCKCOUNT/SIZE before use Paolo Bonzini
2021-06-15 16:50 ` Max Reitz
2021-06-15 16:57 ` Daniel P. Berrangé
2021-06-07 13:52 ` [PATCH v3 0/7] block: file-posix queue Maxim Levitsky
2021-06-10 13:40 ` Paolo Bonzini
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