5b15e2ecaf
Notable changes:
* The only big change is the switch to using a custom QIOChannel for
savevm-async, because the previously used QEMUFileOps was dropped.
Changes to the current implementation:
* Switch to vector based methods as required for an IO channel. For
short reads the passed-in IO vector is stuffed with zeroes at the
end, just to be sure.
* For reading: The documentation in include/io/channel.h states that
at least one byte should be read, so also error out when whe are
at the very end instead of returning 0.
* For reading: Fix off-by-one error when request goes beyond end.
The wrong code piece was:
if ((pos + size) > maxlen) {
size = maxlen - pos - 1;
}
Previously, the last byte would not be read. It's actually
possible to get a snapshot .raw file that has content all the way
up the final 512 byte (= BDRV_SECTOR_SIZE) boundary without any
trailing zero bytes (I wrote a script to do it).
Luckily, it didn't cause a real issue, because qemu_loadvm_state()
is not interested in the final (i.e. QEMU_VM_VMDESCRIPTION)
section. The buffer for reading it is simply freed up afterwards
and the function will assume that it read the whole section, even
if that's not the case.
* For writing: Make use of the generated blk_pwritev() wrapper
instead of manually wrapping the coroutine to simplify and save a
few lines.
* Adapt to changed interfaces for blk_{pread,pwrite}:
* a9262f551e ("block: Change blk_{pread,pwrite}() param order")
* 3b35d4542c ("block: Add a 'flags' param to blk_pread()")
* bf5b16fa40 ("block: Make blk_{pread,pwrite}() return 0 on success")
Those changes especially affected the qemu-img dd patches, because
the context also changed, but also some of our block drivers used
the functions.
* Drop qemu-common.h include: it got renamed after essentially
everything was moved to other headers. The only remaining user I
could find for things dropped from the header between 7.0 and 7.1
was qemu_get_vm_name() in the iscsi-initiatorname patch, but it
already includes the header to which the function was moved.
Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>
54 lines
1.6 KiB
Diff
54 lines
1.6 KiB
Diff
From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
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From: Stefan Reiter <s.reiter@proxmox.com>
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Date: Wed, 9 Dec 2020 11:46:57 +0100
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Subject: [PATCH] PVE: block/pbs: fast-path reads without allocation if
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possible
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...and switch over to g_malloc/g_free while at it to align with other
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QEMU code.
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Tracing shows the fast-path is taken almost all the time, though not
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100% so the slow one is still necessary.
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Signed-off-by: Stefan Reiter <s.reiter@proxmox.com>
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Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>
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---
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block/pbs.c | 17 ++++++++++++++---
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1 file changed, 14 insertions(+), 3 deletions(-)
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diff --git a/block/pbs.c b/block/pbs.c
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index 0b05ea9080..c5eb4d5bad 100644
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--- a/block/pbs.c
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+++ b/block/pbs.c
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@@ -200,7 +200,16 @@ static coroutine_fn int pbs_co_preadv(BlockDriverState *bs,
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BDRVPBSState *s = bs->opaque;
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int ret;
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char *pbs_error = NULL;
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- uint8_t *buf = malloc(bytes);
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+ uint8_t *buf;
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+ bool inline_buf = true;
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+
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+ /* for single-buffer IO vectors we can fast-path the write directly to it */
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+ if (qiov->niov == 1 && qiov->iov->iov_len >= bytes) {
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+ buf = qiov->iov->iov_base;
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+ } else {
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+ inline_buf = false;
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+ buf = g_malloc(bytes);
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+ }
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if (offset < 0 || bytes < 0) {
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fprintf(stderr, "unexpected negative 'offset' or 'bytes' value!\n");
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@@ -223,8 +232,10 @@ static coroutine_fn int pbs_co_preadv(BlockDriverState *bs,
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return -EIO;
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}
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- qemu_iovec_from_buf(qiov, 0, buf, bytes);
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- free(buf);
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+ if (!inline_buf) {
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+ qemu_iovec_from_buf(qiov, 0, buf, bytes);
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+ g_free(buf);
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+ }
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return ret;
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}
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