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141 lines
4.6 KiB
Markdown
141 lines
4.6 KiB
Markdown
# Notes about how NX2 handles saving and loading usb profile data
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Executable of v1.54.
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This document outlines the relevant parts regarding how NX2 loads and stores profiles and how this had an impact on the
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design of the patch module `net-profile`, that hooks up usb profile loading over socket to a remote server.
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## Syscall flow
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The game calls the following system calls in order per player, here player 1 (id 0), when loading usb profile data
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(assume all calls are successful here):
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```c
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// Simplified pseudo-like C code omitting non relevant parameters
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fopen("/mnt/0/nx2save.bin")
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fread(fd_save) // stats area
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fread(fd_save) // encrypted area
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fclose(fd_save)
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fopen("/mnt/0/nx2rank.bin")
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fread(fd_rank) // encrypted area
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fclose(fd_rank)
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```
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For saving the profile, this is the call flow:
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```c
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// Simplified pseudo-like C code omitting non relevant parameters
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fopen("/mnt/0/nx2save.bin")
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fseek(fd_save) // beginning
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fwrite(fd_save) // stats area
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fwrite(fd_save) // encrypted area
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fclose(fd_save)
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fopen("/mnt/0/nx2rank.bin")
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fseek(fd_rank) // beginning
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fwrite(fd_rank) // encrypted area
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fclose(fd_rank)
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```
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We can see that in both scenarios, for loading and saving, the game first takes care of a single file before moving on
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to the next one.
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There is another flow that is slightly different when playing World Max. After playing a song in World Max, the game
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writes the changes of the `nx2save.bin` file back:
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```c
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// Simplified pseudo-like C code omitting non relevant parameters
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fopen("/mnt/0/nx2save.bin")
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fseek(fd_save) // beginning
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fwrite(fd_save) // stats area
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fwrite(fd_save) // encrypted area
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fclose(fd_save)
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```
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## Pumpnet RPCs
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The above set the requirements for how pumpnet needs to handle file loading and storing.
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### First solution
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The initial solution was combining the loading and storing process of both files, `nx2save.bin` and `nx2rank.bin`
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into a single download/upload call.
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Load phase:
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```c
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// Simplified pseudo-like C code omitting non relevant parameters
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fopen("/mnt/0/nx2save.bin")
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pumpnet_download_profiles()
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fread(fd_save) // read from buffered data
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fread(fd_save) // read from buffered data
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fclose(fd_save)
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fopen("/mnt/0/nx2rank.bin") // skip, data already buffered
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fread(fd_rank) // read from buffered data
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fclose(fd_rank) // clear all buffers and reset internal state
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```
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Save phase:
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```c
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// Simplified pseudo-like C code omitting non relevant parameters
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fopen("/mnt/0/nx2save.bin")
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pumpnet_download_profiles()
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fseek(fd_save) // seek for buffers
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fwrite(fd_save) // write to buffers
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fwrite(fd_save) // write to buffers
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fclose(fd_save) // skip, do nothing
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fopen("/mnt/0/nx2rank.bin") // skip, data already buffered
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fseek(fd_rank) // seek for buffers
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fwrite(fd_rank) // write to buffers
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pumpnet_upload_profiles()
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fclose(fd_rank) // clear all buffers and reset internal state
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```
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However, with the additional flow during World Max, this solution didn't work and broke internal state handling.
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Modifying this solution to incorporate saving just the `nx2save.bin` file wasn't feasible with the above architecture.
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### Second solution
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Therefore, the pumpnet backend was re-designed to operate on on a single file level and separate for saving and
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loading.
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Load phase:
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```c
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// Simplified pseudo-like C code omitting non relevant parameters
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fopen("/mnt/0/nx2save.bin")
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pumpnet_download_save()
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fread(fd_save) // read from buffered data
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fread(fd_save) // read from buffered data
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fclose(fd_save)
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pumpnet_clear_save_cache()
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fopen("/mnt/0/nx2rank.bin")
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pumpnet_download_rank()
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fread(fd_rank) // read from buffered data
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fclose(fd_rank)
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pumpnet_clear_rank_cache()
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```
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Save phase:
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```c
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// Simplified pseudo-like C code omitting non relevant parameters
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fopen("/mnt/0/nx2save.bin")
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pumpnet_download_save()
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fseek(fd_save) // seek for buffers
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fwrite(fd_save) // write to buffers
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fwrite(fd_save) // write to buffers
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fclose(fd_save)
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pumpnet_upload_save()
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pumpnet_clear_save_cache()
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fopen("/mnt/0/nx2rank.bin")
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fseek(fd_rank) // seek for buffers
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fwrite(fd_rank) // write to buffers
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fclose(fd_rank)
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pumpnet_upload_rank()
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pumpnet_clear_rank_cache()
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```
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Buffer modifications are detected when `fwrite` is called and flagged accordingly that the module is aware of having
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to write back dirty data on the call to `fclose`.
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State handling is also simplified as it only needs to be taken care of on a file level between `fopen` and `fclose`
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calls and not on a multi-file level.
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This solution is definitely more robust and flexible than the previous one that operated on a full profile level.
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However, the call overhead to the remote server is four times higher compared to the previous solution. Considering
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that these calls are not being issued on a high frequency, server load is unlikely to be an issue. |