User-Memory-Access Kernel Services
In a system call or kernel extension running under a user process, data in the user process can be moved in or out of the kernel using the kernel services listed in this section.
The kernel services that are used to move data in or out of the kernel are the copyin and copyout services. The uiomove service is used for scatter and gather operations. If user data is to be referenced asynchronously, such as from an interrupt handler or a kernel process, the cross memory services must be used.
The User-Memory-Access kernel services are:
| Item | Description |
|---|---|
| copyin, copyin64 | Copies data between user and kernel memory. |
| copyinstr, copyinstr64 | Copies a character string (including the terminating null character) from user to kernel space. |
| copyout, copyout64 | Copies data between user and kernel memory. |
| fubyte, fubyte64 | Fetches, or retrieves, a byte of data from user memory. |
| fuword, fuword64 | Fetches, or retrieves, a word of data from user memory. |
| subyte, subyte64 | Stores a byte of data in user memory. |
| suword, suword64 | Stores a word of data in user memory. |
| uiomove | Moves a block of data between kernel space and a space defined by a uio structure. |
| ureadc | Writes a character to a buffer described by a uio structure. |
| uwritec | Retrieves a character from a buffer described by a uio structure. |
Note: The copyin64, copyout64, copyinstr64, fubyte64, fuword64, subyte64,
and suword64 kernel services are defined as macros when compiling
kernel extensions on the 64–bit kernel. The macros invoke the corresponding
kernel services without the "64" suffix.