From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:40702) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1WlyRN-0001DB-M4 for qemu-devel@nongnu.org; Sun, 18 May 2014 06:35:46 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1WlyRE-00038d-H7 for qemu-devel@nongnu.org; Sun, 18 May 2014 06:35:37 -0400 Received: from mail-pa0-x234.google.com ([2607:f8b0:400e:c03::234]:60200) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1WlyRE-00038V-1o for qemu-devel@nongnu.org; Sun, 18 May 2014 06:35:28 -0400 Received: by mail-pa0-f52.google.com with SMTP id fa1so4492710pad.39 for ; Sun, 18 May 2014 03:35:27 -0700 (PDT) Message-ID: <53788CA7.6010901@gmail.com> Date: Sun, 18 May 2014 18:34:15 +0800 From: Jun Li MIME-Version: 1.0 References: <1399739757-3111-1-git-send-email-juli@redhat.com> <5370E574.3000503@redhat.com> In-Reply-To: <5370E574.3000503@redhat.com> Content-Type: multipart/alternative; boundary="------------020301090309080707030303" Subject: Re: [Qemu-devel] [PATCH v3] snapshot: fixed bdrv_get_full_backing_filename can not get correct full_backing_filename List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Eric Blake , Jun Li , qemu-devel@nongnu.org Cc: kwolf@redhat.com, famz@redhat.com, stefanha@redhat.com This is a multi-part message in MIME format. --------------020301090309080707030303 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 05/12/2014 11:15 PM, Eric Blake wrote: > On 05/10/2014 10:35 AM, Jun Li wrote: >> From: Jun Li > I see three different "[PATCH v3]" mails with this subject. To make > sure we are reviewing the right version, it might help to bump to version 4. Yes, I have send v4 of this patch and changed the commit description. > >> This patch fixed the following bug: >> https://bugzilla.redhat.com/show_bug.cgi?id=1084302 . >> >> path_combine can not calculate the correct full path name for backing_file. >> Such as: >> create a snapshot chain: >> sn2->sn1->$BASE_IMG >> backing file is : /home/wookpecker/img.qcow2 >> sn1 : /home/woodpecker/tmp/sn1 >> sn2 : /home/woodpecker/tmp/sn2 >> when create sn2, path_combine can not got a correct path for $BASE_IMG. > I'm having a hard time parsing that. We usually represent backing > chains with the base image on the left: > > base <- sn1 > > Can you show the output of 'qemu-img info --backing-chain > /home/woodpecker/tmp/sn2' to make it a bit more obvious what your setup > is? What command are you issuing that triggers a path_combine that is > getting the wrong result? Sorry, this is the wrong commit description, please see it on v4. In version 4, I describe it just as followings: create a snapshot chain: $BASE_IMG<-sn1<-sn2 backing file is : ./img.qcow2 sn1 : ./tmp/sn1 sn2 : ./tmp/sn2 So, # /opt/qemu-git-arm/bin/qemu-img info --backing-chain ./tmp/sn2 image: ./tmp/sn2 file format: qcow2 virtual size: 10G (10737418240 bytes) disk size: 196K cluster_size: 65536 backing file: ./tmp/sn1 (actual path: /home/lijun/Work/tmp/sn1) Format specific information: compat: 1.1 lazy refcounts: false image: /home/lijun/Work/tmp/sn1 file format: qcow2 virtual size: 10G (10737418240 bytes) disk size: 196K cluster_size: 65536 backing file: ./img.qcow2 (actual path: /home/lijun/Work/img.qcow2) Format specific information: compat: 1.1 lazy refcounts: false image: /home/lijun/Work/img.qcow2 file format: qcow2 virtual size: 10G (10737418240 bytes) disk size: 196K cluster_size: 65536 Format specific information: compat: 1.1 lazy refcounts: false ------------------ Before this patch, # qemu-img create -f qcow2 -b ./img.qcow2 ./tmp/sn1 # qemu-img create -f qcow2 -b ./tmp/sn1 ./tmp/sn2 qemu-img: Could not open './tmp/sn1': No such file or directory > >> In this patch, will check the backing_filename is a symlink or not firstly, >> then return the full(absolute) path via realpath. > This feels fishy to me, and liable to do the wrong thing. I need more > context on how to reproduce the issue you are attempting to fix before I > can even decide if your fix is the right approach. This patch fixed the following bug(*Bug 1084302* -Should improve error info when can't find backing file for snapshot): https://bugzilla.redhat.com/show_bug.cgi?id=1084302 > >> Signed-off-by: Jun Li >> --- >> block.c | 18 +++++++++++++++++- >> 1 file changed, 17 insertions(+), 1 deletion(-) >> >> diff --git a/block.c b/block.c >> index b749d31..6674719 100644 >> --- a/block.c >> +++ b/block.c >> @@ -304,10 +304,26 @@ void path_combine(char *dest, int dest_size, >> >> void bdrv_get_full_backing_filename(BlockDriverState *bs, char *dest, size_t sz) >> { >> + struct stat sb; >> + char *linkname; >> + >> if (bs->backing_file[0] == '\0' || path_has_protocol(bs->backing_file)) { >> pstrcpy(dest, sz, bs->backing_file); >> } else { >> - path_combine(dest, sz, bs->filename, bs->backing_file); >> + if (lstat(bs->backing_file, &sb) == -1) { >> + perror("lstat"); >> + exit(EXIT_FAILURE); >> + } >> + >> + /* Check linkname is a link or not */ >> + if (S_ISLNK(sb.st_mode)) { >> + linkname = malloc(sb.st_size + 1); >> + readlink(bs->backing_file, linkname, sb.st_size + 1); >> + linkname[sb.st_size] = '\0'; >> + realpath(linkname, dest); >> + } else { >> + realpath(bs->backing_file, dest); >> + } > Why are you tweaking just this caller, instead of path_combine() to > affect all other callers? I will check. Thx. Best Regards, Jun Li --------------020301090309080707030303 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: 8bit
On 05/12/2014 11:15 PM, Eric Blake wrote:
On 05/10/2014 10:35 AM, Jun Li wrote:

From: Jun Li <junmuzi@gmail.com>

I see three different "[PATCH v3]" mails with this subject.  To make
sure we are reviewing the right version, it might help to bump to version 4.
Yes, I have send v4 of this patch and changed the commit description.


This patch fixed the following bug:
https://bugzilla.redhat.com/show_bug.cgi?id=1084302 .

path_combine can not calculate the correct full path name for backing_file.
Such as:
create a snapshot chain:
sn2->sn1->$BASE_IMG
backing file is : /home/wookpecker/img.qcow2
sn1 : /home/woodpecker/tmp/sn1
sn2 : /home/woodpecker/tmp/sn2
when create sn2, path_combine can not got a correct path for $BASE_IMG.

I'm having a hard time parsing that.  We usually represent backing
chains with the base image on the left:

base <- sn1

Can you show the output of 'qemu-img info --backing-chain
/home/woodpecker/tmp/sn2' to make it a bit more obvious what your setup
is?  What command are you issuing that triggers a path_combine that is
getting the wrong result?
Sorry, this is the wrong commit description, please see it on v4. In version 4, I describe it just as followings:
create a snapshot chain:
$BASE_IMG<-sn1<-sn2
backing file is : ./img.qcow2
sn1 : ./tmp/sn1
sn2 : ./tmp/sn2

So,
# /opt/qemu-git-arm/bin/qemu-img info --backing-chain ./tmp/sn2
image: ./tmp/sn2
file format: qcow2
virtual size: 10G (10737418240 bytes)
disk size: 196K
cluster_size: 65536
backing file: ./tmp/sn1 (actual path: /home/lijun/Work/tmp/sn1)
Format specific information:
    compat: 1.1
    lazy refcounts: false

image: /home/lijun/Work/tmp/sn1
file format: qcow2
virtual size: 10G (10737418240 bytes)
disk size: 196K
cluster_size: 65536
backing file: ./img.qcow2 (actual path: /home/lijun/Work/img.qcow2)
Format specific information:
    compat: 1.1
    lazy refcounts: false

image: /home/lijun/Work/img.qcow2
file format: qcow2
virtual size: 10G (10737418240 bytes)
disk size: 196K
cluster_size: 65536
Format specific information:
    compat: 1.1
    lazy refcounts: false
------------------
Before this patch,
# qemu-img create -f qcow2 -b ./img.qcow2  ./tmp/sn1
# qemu-img create -f qcow2 -b ./tmp/sn1 ./tmp/sn2
qemu-img: Could not open './tmp/sn1': No such file or directory

 


In this patch, will check the backing_filename is a symlink or not firstly,
then return the full(absolute) path via realpath.

This feels fishy to me, and liable to do the wrong thing.  I need more
context on how to reproduce the issue you are attempting to fix before I
can even decide if your fix is the right approach.
This patch fixed the following bug(Bug 1084302 - Should improve error info when can't find backing file for snapshot):
https://bugzilla.redhat.com/show_bug.cgi?id=1084302


Signed-off-by: Jun Li <junmuzi@gmail.com>
---
 block.c | 18 +++++++++++++++++-
 1 file changed, 17 insertions(+), 1 deletion(-)

diff --git a/block.c b/block.c
index b749d31..6674719 100644
--- a/block.c
+++ b/block.c
@@ -304,10 +304,26 @@ void path_combine(char *dest, int dest_size,
 
 void bdrv_get_full_backing_filename(BlockDriverState *bs, char *dest, size_t sz)
 {
+    struct stat sb;
+    char *linkname;
+
     if (bs->backing_file[0] == '\0' || path_has_protocol(bs->backing_file)) {
         pstrcpy(dest, sz, bs->backing_file);
     } else {
-        path_combine(dest, sz, bs->filename, bs->backing_file);
+        if (lstat(bs->backing_file, &sb) == -1) {
+            perror("lstat");
+            exit(EXIT_FAILURE);
+        }
+
+        /* Check linkname is a link or not */
+        if (S_ISLNK(sb.st_mode)) {
+            linkname = malloc(sb.st_size + 1);
+            readlink(bs->backing_file, linkname, sb.st_size + 1);
+            linkname[sb.st_size] = '\0';
+            realpath(linkname, dest);
+        } else {
+            realpath(bs->backing_file, dest);
+        }

Why are you tweaking just this caller, instead of path_combine() to
affect all other callers?
I will check. Thx.

Best Regards,
Jun Li
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