[in_node_exporter_meterics/ne_filesystem_linux.c] reports incorrect available / free size in bytes

[tswaehn]

Bug Report

Describe the bug

compared to the output of stat -f which uses the same library:

$ stat -f /storagebox/
  File: "/storagebox/"
    ID: 0        Namelen: 255     Type: fuseblk
Block size: 131072     Fundamental block size: 512
Blocks: Total: 2147483648 Free: 1457905063 Available: 1457905063
Inodes: Total: 1457930588 Free: 1457905063

we get an actual disc size of: 1TB = (2147483648 * 512) = (Blocks Total * Fundamental block size) - correct

however the plugin uses the optimal transfer block size in this case 131072, so the the reported disc size is: 280TB - wrong

Replication Procedure

• for most discs the optimal block size and the fundamental block size are equal, so the output will be correct in most cases.
• however in the case they are not same the output is 100% incorrect.

Your Environment

PRETTY_NAME="Debian GNU/Linux 12 (bookworm)"
NAME="Debian GNU/Linux"
VERSION_ID="12"
VERSION="12 (bookworm)"
VERSION_CODENAME=bookworm
ID=debian
HOME_URL="https://www.debian.org/"
SUPPORT_URL="https://www.debian.org/support"
BUG_REPORT_URL="https://bugs.debian.org/

Linux dev-debian 6.1.0-18-amd64 #1 SMP PREEMPT_DYNAMIC Debian 6.1.76-1 (2024-02-01) x86_64 GNU/Linux

[patrick-stephens]

Please follow the template for PRs to capture all relevant details - in this case the config and version of FB would be super helpful.

[tswaehn]

It's an issue with the latest main source code.

Package: fluent-bit
Version: 3.2.5
Priority: optional
Section: devel
Maintainer: Eduardo Silva <[email protected]>

# System - Complete Node Metrics
[INPUT]
    name                        node_exporter_metrics
    tag                         gateway_metrics
    scrape_interval             5s 

[tswaehn]

the issue is here

https://github.com/fluent/fluent-bit/blob/e2461d63cbebb7567549c092976012c543553231/plugins/in_node_exporter_metrics/ne_filesystem_linux.c#L217C21-L217C73

result = statfs(field_values[1], &mount_point_info);

and here

fluent-bit/plugins/in_node_exporter_metrics/ne_filesystem_linux.c

Line 249 in e2461d6

cmt_gauge_set(ctx->fs_free_bytes,

                        cmt_gauge_set(ctx->fs_free_bytes,
                                      timestamp,
                                      mount_point_info.f_bsize *
                                      mount_point_info.f_bfree,
                                      3, labels);

where statfs() delivers the "optimal blocksize" however not the physical block size, refer to:

https://www.man7.org/linux/man-pages/man2/statfs.2.html