[CRIU] [PATCH] pagemap: fix reading pages from socket for --remote case

[Mike Rapoport]

On Tue, Apr 25, 2017 at 08:56:19AM +0100, Rodrigo Bruno wrote:
> Hi,
> 
> 2017-04-24 18:00 GMT+01:00 Pavel Emelyanov <xemul at virtuozzo.com>:
> 
> > >>
> > >> Maybe it's better to introduce separate ->maybe_read_page callback for
> > opts.remote case?
> > >> This would let us localize the cache/proxy pages reading code in one
> > place.
> > >
> > > Well, we could. E.g. something like the patch below (untested). Note that
> > > we already have maybe_read_page_remote for the remote lazy restore case,
> > > and, ideally, the cache/proxy and lazy cases should use the same code to
> > > read pages.
> >
> > Yup. I like this patch :)
> > Rodrigo, what do you think?
> >
> 
> I agree.

All right, below is the more formal version of the patch. I'd suggest to
start with it to make --remote able to restore the memory. The next step
related to --remote and the page-read would be to see if it's possible to
use ASYNC with sockets, what should be refactored to enable it and how we
reduce code and functionality duplication.

 
>From 645c2f8e5afe090ee362d3225b97e2b5f1bc95cb Mon Sep 17 00:00:00 2001
From: Mike Rapoport <rppt at linux.vnet.ibm.com>
Date: Fri, 21 Apr 2017 17:29:10 +0300
Subject: [CRIU][PATCH v3] pagemap: fix reading pages from socket for --remote case

When --remote option is specified, read_local_page tries to pread from a
socket, and fails with "Illegal seek" error.
Restore single pread call for regular image files case and introduce
maybe_read_page_img_cache version of maybe_read_page method.

Generally-approved-by: Rodrigo Bruno <rbruno at gsd.inesc-id.pt>
Signed-off-by: Mike Rapoport <rppt at linux.vnet.ibm.com>
---
v3: use different ->maybe_read_page method for --remote case
v2: simplify call to pread in non-remote case, it does not need 'curr'

 criu/pagemap.c | 52 +++++++++++++++++++++++++++++++++++++++++-----------
 1 file changed, 41 insertions(+), 11 deletions(-)

diff --git a/criu/pagemap.c b/criu/pagemap.c
index 6c741b4..353c469 100644
--- a/criu/pagemap.c
+++ b/criu/pagemap.c
@@ -255,7 +255,6 @@ static int read_local_page(struct page_read *pr, unsigned long vaddr,
 {
 	int fd = img_raw_fd(pr->pi);
 	int ret;
-	size_t curr = 0;
 
 	/*
 	 * Flush any pending async requests if any not to break the
@@ -265,15 +264,10 @@ static int read_local_page(struct page_read *pr, unsigned long vaddr,
 		return -1;
 
 	pr_debug("\tpr%d-%u Read page from self %lx/%"PRIx64"\n", pr->pid, pr->id, pr->cvaddr, pr->pi_off);
-	while (1) {
-		ret = pread(fd, buf + curr, len - curr, pr->pi_off + curr);
-		if (ret < 1) {
-			pr_perror("Can't read mapping page %d", ret);
-			return -1;
-		}
-		curr += ret;
-		if (curr == len)
-			break;
+	ret = pread(fd, buf, len, pr->pi_off);
+	if (ret != len) {
+		pr_perror("Can't read mapping page %d", ret);
+		return -1;
 	}
 
 	if (opts.auto_dedup) {
@@ -390,6 +384,40 @@ static int maybe_read_page_local(struct page_read *pr, unsigned long vaddr,
 	return ret;
 }
 
+static int maybe_read_page_img_cache(struct page_read *pr, unsigned long vaddr,
+				     int nr, void *buf, unsigned flags)
+{
+	unsigned long len = nr * PAGE_SIZE;
+	int fd = img_raw_fd(pr->pi);
+	int ret;
+	size_t curr = 0;
+
+	pr_debug("\tpr%d-%u Read page from self %lx/%"PRIx64"\n", pr->pid, pr->id, pr->cvaddr, pr->pi_off);
+	while (1) {
+		ret = read(fd, buf + curr, len - curr);
+		if (ret < 0) {
+			pr_perror("Can't read mapping page %d", ret);
+			return -1;
+		}
+		curr += ret;
+		if (curr == len)
+			break;
+	}
+
+	if (opts.auto_dedup) {
+		ret = punch_hole(pr, pr->pi_off, len, false);
+		if (ret == -1)
+			return -1;
+	}
+
+	if (ret == 0 && pr->io_complete)
+		ret = pr->io_complete(pr, vaddr, nr);
+
+	pr->pi_off += len;
+
+	return ret;
+}
+
 static int read_page_complete(int pid, unsigned long vaddr, int nr_pages, void *priv)
 {
 	int ret = 0;
@@ -803,7 +831,9 @@ int open_page_read_at(int dfd, int pid, struct page_read *pr, int pr_flags)
 	pr->id = ids++;
 	pr->pid = pid;
 
-	if (remote)
+	if (opts.remote)
+		pr->maybe_read_page = maybe_read_page_img_cache;
+	else if (remote)
 		pr->maybe_read_page = maybe_read_page_remote;
 	else
 		pr->maybe_read_page = maybe_read_page_local;
-- 
1.9.1