Method and system for hybrid direct input/output (I/O) with a storage device

1. A non-transitory computer readable medium comprising instructions, which when executed by a processor perform a method, the method comprising:

intercepting, in a user-level of a host, an open file request (OFR) for a file issued by an application to a file system (FS);

forwarding the OFR to the FS, wherein the FS is located in the user-level and the OFR is forwarded to the FS via a kernel module in a kernel-level of the host;

receiving from the FS, in response to the OFR, a file descriptor (FD) for the file;

issuing a status request (SR) for the file to the FS, wherein the SR comprises the file descriptor;

receiving from the FS, in response to the SR, status information for a target device on which the file is located, wherein the status information comprises an object identified (OID) for the file, wherein the target device is external to the host;

storing a mapping of FD to the OID;

after storing the mapping of the FD to the OID:

intercepting, by a direct I/O library, a first file operation request (FOR) for the file, wherein the request comprises the FD;

making a first determination that the first FOR is one selected from a group consisting of a read request and a write request;

based on the first determination, making a second determination that the target device on which the file is located supports the direct I/O protocol;

issuing a direct I/O request to the target device using the OID for the file, wherein the direct I/O request is not processed by the FS;

intercepting, by the direct I/O library, a second FOR for the file, wherein the second FOR comprises the FD;

making a third determination that the second FOR is not one selected from a group consisting of the read request and the write request; and

based on the third determination, forwarding the second FOR to the FS via the kernel module in the kernel-level of the host.

2. The non-transitory computer readable medium of claim 1 , the method further comprising:

receiving a notification, in response to the direct I/O request, that the direct I/O request is completed, wherein the notification is sent directly from the target device to the host and wherein the FS does not receive the notification.

3. The non-transitory computer readable medium of claim 1 , the method further comprising:

creating a unified address space comprising a memory location on the target device prior to the issuance of the direct I/O request,

wherein issuing the direct I/O request comprises storing the direct I/O request directly in the memory location on the target device.

4. The non-transitory computer readable medium of claim 1 , wherein issuing the direct I/O request to the target device comprises storing the direct I/O request in a memory location on the target storage device, wherein the memory location is part of a unified address space that is directly accessible by the host.

5. The non-transitory computer readable medium of claim 4 , wherein the memory location is associated with a submission queue.

6. A system, comprising:

a processor;

a user-level comprising an application, a direct I/O library, and a file system (FS);

a virtual file system (VFS) in the kernel-level, wherein the VFS is interposed between the direct I/O library and the kernel module;

a kernel-level, executing on the processor, comprising a kernel module; and

wherein the application is configured to issue an open file request (OFR) for a file;

wherein the direct I/O library is configured to intercept the OFR and forward the OFR to the VFS;

wherein the VFS is configured to forward to the OFR to the kernel module;

wherein the kernel module is configured to forward the OFR to the FS;

wherein the FS is configured to obtain a file descriptor (FD) for the file and send the FD to the direct I/O library via the kernel module;

wherein the direct I/O library is further configured to issue a status request (SR) for the file to the FS, wherein the SR comprises the file descriptor;

wherein the FS is configured to receive, via the kernel module, the SR and generate status information for a target device on which the file is located, wherein the status information comprises an object identified (OID) for the file and specifies that the target device supports a direct I/O protocol, and send the status information to the direct I/O library via the kernel module;

wherein the direct I/O library is further configured to receive the status information and store a mapping of FD to the OID;

wherein the target device is operatively connected to the system; and

wherein the kernel module is a File system in USEr space (FUSE) module.

7. The system of claim 6 , wherein the direct I/O library is further configured to:

after storing the mapping of the FD to the OID:

intercept a first file operation request (FOR) for the file, wherein the request comprises the FD;

make a first determination that the first FOR is one selected from a group consisting of a read request and a write request;

based on the first determination, make a second determination that the target device on which the file is located supports the direct I/O protocol; and

issue a direct I/O request to the target device using the OID for the file, wherein the direct I/O request is not processed by the FS and is not processed by the kernel module.

8. The system of claim 7 , further comprising:

a kernel-level direct I/O library configured to create a unified address space comprising a memory location on the target device prior to the issuance of the direct I/O request, wherein issuing the direct I/O request comprises storing the direct I/O request directly in the memory location on the target device.

9. The system of claim 7 , wherein the unified address is implemented using PCIe and a non-transparent bridge interposed between the system and the target device.

10. The system of claim 6 , wherein the direct I/O library is further configured to:

after storing the mapping of the FD to the OID:

receive a second FOR for the file, wherein the second FOR comprises the FD;

make a third determination that the second FOR is not one selected from a group consisting of the read request and the write request;

based on the third determination, forward the second FOR to the FS via the kernel module.

11. The system of claim 10 , wherein the second FOR is one selected from a group consisting of a modify operation and a delete operation.

12. The system of claim 10 , wherein the FS is further configured to:

receive the second FOR;

service the second FOR using the direct I/O library to generate a response;

sending the response to the application via the kernel module and the direct I/O library.

13. The system of claim 6 , wherein the target device comprises persistent storage.

14. The system of claim 13 , wherein the persistent storage comprises a solid state memory device.