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Description of problem:
It is impossible to resize a file with preallocation=full, if its current size would correspond to a negative number when represented as an int32
eg create a 5GB raw file initially
$ qemu-img create -f raw demo.img 5G
Formatting 'demo.img', fmt=raw size=5368709120
We can successfully extend it one 1GB in size
$ qemu-img resize -f raw --preallocation=full demo.img +1G
Image resized.
But trying to further extend it fails
$ qemu-img resize -f raw --preallocation=full demo.img +1G
qemu-img: Failed to seek to the old end of file: Invalid argument
If you strace it, we can see the lseek() succeeded, despite the message
$ strace -e trace=lseek qemu-img resize -f raw --preallocation=full demo.img +1G
lseek(10, 0, SEEK_END) = 6442450944
lseek(10, 6442450944, SEEK_SET) = 6442450944
qemu-img: Failed to seek to the old end of file: Invalid argument
+++ exited with 1 +++
The problem appears to be caused by this commit:
commit d0bc9e5d5e86d5dd566e2d967af8476cee351c93
Author: Max Reitz <mreitz>
Date: Tue Jun 13 22:20:58 2017 +0200
block/file-posix: Generalize raw_regular_truncate
which added this bit of code to the preallocation=full
+ result = lseek(fd, current_length, SEEK_SET);
+ if (result < 0) {
+ result = -errno;
+ error_setg_errno(errp, -result,
+ "Failed to seek to the old end of file");
+ goto out;
+ }
+
The 'result' variable here is a plain 'int', so 32-bits, causing the lseek result to overflow & wrap around.
This patch is new in QEMU 2.10.0, so would be a regression compared to earlier 7.x releases.
Version-Release number of selected component (if applicable):
qemu-kvm-rhev-2.10.0-21.el7.x86_64
Hi Daniel,
I cannot reproduce the bug. The issue i met is that further extending passed, but the image is not fully allocated. It should be same issue as the bug 1537985.
Version-Release number of selected component:
qemu-kvm-rhev-2.10.0-21.el7
kernel-3.10.0-856.el7.x86_64
Test steps:
1. Create the image.
# qemu-img create -f raw demo.img 5G
Formatting 'demo.img', fmt=raw size=5368709120
2. Extend the image with 'full' mode, and the image is grown with full allocated.
# qemu-img resize -f raw --preallocation=full demo.img +1G
Image resized.
# qemu-img map --output=json demo.img
[{ "start": 0, "length": 5368709120, "depth": 0, "zero": true, "data": false, "offset": 0},
{ "start": 5368709120, "length": 1073741824, "depth": 0, "zero": false, "data": true, "offset": 5368709120}]
3. Further extend the image with 'full' mode. The command passed but the image isn't grown with full allocated.
# strace -e trace=lseek qemu-img resize -f raw --preallocation=full demo.img +1G
lseek(10, 0, SEEK_END) = 6442450944
lseek(10, 6442450944, SEEK_SET) = 6442450944
lseek(10, 0, SEEK_END) = 7516192768
Image resized.
+++ exited with 0 +++
# qemu-img map --output=json demo.img
[{ "start": 0, "length": 5368709120, "depth": 0, "zero": true, "data": false, "offset": 0},
{ "start": 5368709120, "length": 1073741824, "depth": 0, "zero": false, "data": true, "offset": 5368709120},
{ "start": 6442450944, "length": 1073741824, "depth": 0, "zero": true, "data": false, "offset": 6442450944}]
I think your result can be explained by the flawed code I identified. It sets 'result = -errno' when it gets integer wraparound. The 'lseek' syscall did not fail though, so this 'errno' value is going to be completely random garbage - in fact it could even be 'zero' in which case it will skip the preallocation logic thinking it has an error, but then return 0 from this method indicating success to the caller.
Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.
For information on the advisory, and where to find the updated
files, follow the link below.
If the solution does not work for you, open a new bug report.
https://access.redhat.com/errata/RHBA-2018:3443
Description of problem: It is impossible to resize a file with preallocation=full, if its current size would correspond to a negative number when represented as an int32 eg create a 5GB raw file initially $ qemu-img create -f raw demo.img 5G Formatting 'demo.img', fmt=raw size=5368709120 We can successfully extend it one 1GB in size $ qemu-img resize -f raw --preallocation=full demo.img +1G Image resized. But trying to further extend it fails $ qemu-img resize -f raw --preallocation=full demo.img +1G qemu-img: Failed to seek to the old end of file: Invalid argument If you strace it, we can see the lseek() succeeded, despite the message $ strace -e trace=lseek qemu-img resize -f raw --preallocation=full demo.img +1G lseek(10, 0, SEEK_END) = 6442450944 lseek(10, 6442450944, SEEK_SET) = 6442450944 qemu-img: Failed to seek to the old end of file: Invalid argument +++ exited with 1 +++ The problem appears to be caused by this commit: commit d0bc9e5d5e86d5dd566e2d967af8476cee351c93 Author: Max Reitz <mreitz> Date: Tue Jun 13 22:20:58 2017 +0200 block/file-posix: Generalize raw_regular_truncate which added this bit of code to the preallocation=full + result = lseek(fd, current_length, SEEK_SET); + if (result < 0) { + result = -errno; + error_setg_errno(errp, -result, + "Failed to seek to the old end of file"); + goto out; + } + The 'result' variable here is a plain 'int', so 32-bits, causing the lseek result to overflow & wrap around. This patch is new in QEMU 2.10.0, so would be a regression compared to earlier 7.x releases. Version-Release number of selected component (if applicable): qemu-kvm-rhev-2.10.0-21.el7.x86_64