Syscalls: add support for memfd_create #2005
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This change moves the call to filesystem_update_mtime() from the truncate callback of filesystem drivers to the generic filesystem code that invokes the callback. Beside removing duplicated code, this change will allow building filesystem drivers as klibs (which cannot call the now() function directly because it references the __vdso_vdso_dat hidden symbol).
This change allows creating temporary files (i.e. files that are not associated to a directory entry and are deleted when closed) on filesystems other than TFS. The create callback of existing filesystem drivers has been amended to be able to create temporary files (or return FS_STATUS_INVAL if this feature is not supported). This change will be needed when support for memfd_create() is added.
This function undoes what filesystem_init() does; it is used in the TFS code when destroying a filesystem, instead of calling directly pagecache_dealloc_volume().
Code that uses a file table to enumerate file metadata tuples and to establish a correspondence between metadata tuples and fsfile structs has been moved from tfs.c to fs.c and fs.h. It will be reused when implementing tmpfs.
The body of this new function has been extracted from open_internal(). This change will allow userspace to open regular files via syscalls other than open() and similar, i.e. syscalls that do not reference a filesystem path, such as memfd_create(). The file struct has been modified to embed all fdesc closures, so that individual allocations and deallocations for each closure when opening and closing a file are no longer necessary.
This macro is a more lightweight version of register_syscall(), and can be used to initialize the name and flags of a syscall without configuring a handler. It is now used for all non-supported syscalls. If a klib implementing additional syscalls is loaded, it can call swap_syscall_handler() instead of register_syscall().
This dependency is already listed in the run targets of the top- level Makefile; having this dependency also in the platform Makefiles causes the disk image to be created twice at each execution of a runtime test.
This syscall creates an anonymous file that behaves like a regular file, and so can be modified, truncated, memory-mapped, and so on, but, unlike a regular file, lives in RAM and has a volatile backing storage. This syscall is implemented in a new "shmem" klib, which is meant to contain the implementation of all shared-memory features in the kernel. The memfd implementation relies on an underlying tmpfs filesystem, which is implemented in another new klib named "tmpfs" (which in the future can be used to create arbitrary RAM-backed filesystems and mount them at arbitrary locations in the root filesystem). Closes #1986.
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This syscall creates an anonymous file that behaves like a regular file, and so can be modified, truncated, memory-mapped, and so on, but, unlike a regular file, lives in RAM and has a volatile backing storage.
This syscall is implemented in a new "shmem" klib, which is meant to contain the implementation of all shared-memory features in the kernel. The memfd implementation relies on an underlying tmpfs filesystem, which is implemented in another new klib named "tmpfs" (which in the future can be used to create arbitrary RAM-backed filesystems and mount them at arbitrary locations in the root filesystem).
Closes #1986.