The file-read command of the QEMU guest agent previously had several practical limitations. It always read a fixed 16 MiB block starting at offset 0, making it impossible to retrieve larger files in multiple chunks. On busy or resource‑constrained hosts, requests for large files often timed out because the agent attempted to read and JSON‑encode the entire 16 MiB block at once (while producing high CPU load in both qemu-guest-agent, as well as pvedaemon).
Since decode wasn't optional, readinb binary data encoded as JSON string regularly caused highly inflated payload sizes due to extensive unicode escaping. This series extends the file-read method with three new parameters: - decode — Controls whether the base64‑encoded data returned by the guest agent should be decoded before being sent back through the API. When disabled, the base64 string is passed through unchanged, which is ideal for binary data and mirrors the existing encode parameter of file-write. - offset — Allows reading from an arbitrary byte offset within the file. - count — Allows requesting a smaller number of bytes than the internal 16 MiB limit, granting more flexibility to avoid API timeouts. With these additions, the agent/file-read API now essentially behaves like a pread() systemcall. All parameter additions were done in a backwards-compatible fashion. Markus Ebner (3): agent: file-read: Allow specifying max number of bytes to read agent: file-read: Allow maintaining base64-encoding of content agent: file-read: Allow specifying byte offset to start reading at src/PVE/API2/Qemu/Agent.pm | 60 +++++++++++++++++++++++++++++++++----- 1 file changed, 52 insertions(+), 8 deletions(-) -- 2.53.0
