76 lines
2.3 KiB
C
76 lines
2.3 KiB
C
#ifndef VLIBC_SYS_UIO_H
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#define VLIBC_SYS_UIO_H
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/*
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* vlibc — <sys/uio.h>.
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*
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* Scatter/gather I/O: readv() and writev() transfer data between a file
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* descriptor and a vector of memory buffers (POSIX.1-2008 base). Both are
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* unbuffered pass-throughs to the kernel: the iovec array is handed to
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* SYS_readv/SYS_writev as-is, and the kernel applies its own validation
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* (iovcnt in 0..IOV_MAX, iov NULL with iovcnt > 0 faults as EFAULT). Failures
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* are reported as -1 with errno set by the syscall layer.
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*
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* Level 1 (onlyposix): readv, writev.
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*
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* The Linux extensions that build on this ABI (preadv/pwritev,
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* process_vm_readv/process_vm_writev, ...) are deliberately absent — they are
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* not POSIX and belong to a later compatibility profile.
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*
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* struct iovec matches the kernel's struct iovec (x86_64: a pointer and a
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* size_t, no padding). IOV_MAX is 1024, the Linux UIO_MAXIOV; the kernel
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* rejects any iovcnt above it with EINVAL.
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*
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* None of these declarations carry an intent attribute: every function
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* performs I/O with side effects and reports failures through errno, so
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* const/pure would be unsound.
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*/
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#include <vlibc/features.h>
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#include <stddef.h>
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#include <sys/types.h>
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#ifdef __cplusplus
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extern "C" {
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#endif
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/* Maximum number of iovec entries a single readv()/writev() call accepts. */
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#define IOV_MAX 1024
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/*
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* A scatter/gather segment: iov_base points at the buffer (or, for readv,
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* the buffer to fill) and iov_len is its size in bytes. Kernel layout, as
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* above.
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*/
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struct iovec
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{
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void *iov_base; /* starting address of the segment */
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size_t iov_len; /* number of bytes in the segment */
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};
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/*
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* Read up to the sum of iov_len bytes from fd into the iovcnt buffers of
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* iov, in order; return the number of bytes read, 0 at end of file, or -1
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* with errno set on error. Buffers are filled completely before the next
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* one is touched.
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*/
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ssize_t
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readv(int fd, const struct iovec *iov, int iovcnt);
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/*
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* Write up to the sum of iov_len bytes from the iovcnt buffers of iov to
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* fd, in order; return the number of bytes written, or -1 with errno set
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* on error. The kernel applies its own validation (iovcnt 0..IOV_MAX, iov
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* NULL with iovcnt > 0 faults as EFAULT).
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*/
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ssize_t
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writev(int fd, const struct iovec *iov, int iovcnt);
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#ifdef __cplusplus
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}
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#endif
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#endif /* VLIBC_SYS_UIO_H */
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