Shared filesystem metadata caching

A method comprising:

• receiving, by a first storage controller (SC) included in a first guest, a first metadata request associated with a first file stored in a host memory of a host of the first guest and a second guest;
• retrieving, by the first SC, a first version identifier (VID) of first metadata associated with the first file from a first metadata cache included in a paravirtualized storage device in the first guest;
• validating, by the first SC, the first VID against a corresponding second VID in a registration table (RT) stored in the host memory, wherein the RT is mapped into a first memory space of the first guest and a second memory space of the second guest;
• responsive to determining that the first VID matches the second VID, responding to the first metadata request based on the first metadata in the first metadata cache;
• and
• responsive to determining that the first VID fails to match the second VID, sending a second metadata request to a first filesystem daemon (FSD) via a paravirtualization protocol, based on the first metadata request, to update the first metadata;
• updating the first VID to match the second VID;
• and
• responding to the first metadata request based on the updated first metadata.

A system comprising:

• a host with (i) a processor, (ii) a first guest, including a first storage controller (SC) and a paravirtualized storage device including a first metadata cache, associated with a first filesystem daemon (FSD), (iii) a second guest associated with a second FSD, (iv) a registration server, and (v) a host memory with a registration table (RT), where the RT is mapped into a first memory space of the first guest and a second memory space of the second guest, wherein the registration server is configured to:
• create a first RT entry associated with a first file stored in the host memory in the RT based on a file request associated with the first file received from the first SC by the first FSD;
• set a first version identifier (VID) in the first RT entry to an initial value,
• wherein the second FSD is configured to:
• update the first VID in response to the second guest requesting to modify the first file, and
• wherein the first SC is configured to:
• determine that first metadata of the first file in the first metadata cache requires updating based on a corresponding second VID stored in the first metadata cache failing to match the updated first VID.