Efficiently providing a guest context access to file content at a host context

A method, implemented at a computer system that includes at least one processor, for using metadata for a contentless file to provide a guest context access to file content, the method comprising:

• within a guest context at the computer system:
• mounting a first filesystem namespace from a container image that includes (i) metadata defining one or more filesystem properties of a first file contained within the first filesystem namespace, the container image lacking content of the first file;
• and (ii) mapping data that includes information usable to identify a second file within a second filesystem namespace that is external to the guest context, and from which the content of the first file is obtainable;
• based on the one or more filesystem properties of the first file, performing a filesystem operation involving the first file without switching to a host context at the computer system;
• and
• based on the one or more filesystem properties of the first file, responding to a requested access to the content of the first file, including:
• based on the mapping data, communicating, to the host context, a request for the host context to supply the content of the first file to the guest context;
• and
• after returning from a context switch to the host context, responding to the requested access based at least on supplying content of the second file from one or more guest context memory pages, the one or more guest context memory pages mapped to one or more host context memory pages containing the content of the second file.

A computer system that includes at least one processor and a computer readable media having stored thereon computer-executable instructions that are executable by the at least one processor to cause the computer system to perform a method for using metadata for a contentless file to provide a guest context access to file content, the method comprising, within a guest context at the computer system:

• mounting a first filesystem namespace from a container image that includes (i) metadata defining one or more filesystem properties of a first file contained within the first filesystem namespace, the container image lacking content of the first file;
• and (ii) mapping data that includes information usable to identify a second file within a second filesystem namespace that is external to the guest context, and from which the content of the first file is obtainable;
• based on the one or more filesystem properties of the first file, performing a filesystem operation involving the first file without switching to a host context at the computer system;
• and
• based on the one or more filesystem properties of the first file, responding to a requested access to the content of the first file, including:
• based on the mapping data, communicating, to the host context, a request for the host context to supply the content of the first file to the guest context;
• and
• after returning from a context switch to the host context, responding to the requested access based at least on supplying content of the second file from one or more guest context memory pages, the one or more guest context memory pages mapped to one or more host context memory pages containing the content of the second file.

A computer readable media having stored thereon computer-executable instructions that are executable by at least one processor to cause a computer system to perform a method for using metadata for a contentless file to provide a guest context access to file content, the method comprising, within a guest context at the computer system:

• mounting a first filesystem namespace from a container image that includes (i) metadata defining one or more filesystem properties of a first file contained within the first filesystem namespace, the container image lacking content of the first file;
• and (ii) mapping data that includes information usable to identify a second file within a second filesystem namespace that is external to the guest context, and from which the content of the first file is obtainable;
• based on the one or more filesystem properties of the first file, performing a filesystem operation involving the first file without switching to a host context at the computer system;
• and
• based on the one or more filesystem properties of the first file, responding to a requested access to the content of the first file, including:
• based on the mapping data, communicating, to the host context, a request for the host context to supply the content of the first file to the guest context;
• and
• after returning from a context switch to the host context, responding to the requested access based at least on supplying content of the second file from one or more guest context memory pages, the one or more guest context memory pages mapped to one or more host context memory pages containing the content of the second file.