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28 .\" @(#)read.2 8.4 (Berkeley) 2/26/94
29 .\" $FreeBSD: src/lib/libc/sys/read.2,v 1.9.2.6 2001/12/14 18:34:01 ru Exp $
30 .\" $DragonFly: src/lib/libc/sys/read.2,v 1.5 2006/04/27 16:01:33 swildner Exp $
48 .Fn read "int d" "void *buf" "size_t nbytes"
50 .Fn readv "int d" "const struct iovec *iov" "int iovcnt"
52 .Fn pread "int d" "void *buf" "size_t nbytes" "off_t offset"
54 .Fn preadv "int d" "const struct iovec *iov" "int iovcnt" "off_t offset"
59 of data from the object referenced by the descriptor
61 into the buffer pointed to by
64 performs the same action, but scatters the input data
67 buffers specified by the members of the
69 array: iov[0], iov[1], ..., iov[iovcnt\|\-\|1].
74 calls perform the same function, but read from the specified position in
75 the file without modifying the file pointer.
83 structure is defined as:
85 .Bd -literal -offset indent -compact
87 char *iov_base; /* Base address. */
88 size_t iov_len; /* Length. */
94 entry specifies the base address and length of an area
95 in memory where data should be placed.
99 will always fill an area completely before proceeding
102 On objects capable of seeking, the
105 given by the pointer associated with
111 the pointer is incremented by the number of bytes actually read.
113 Objects that are not capable of seeking always read from the current
114 position. The value of the pointer associated with such an
117 Upon successful completion,
123 return the number of bytes actually read and placed in the buffer.
124 The system guarantees to read the number of bytes requested if
125 the descriptor references a normal file that has that many bytes left
126 before the end-of-file, but in no other case.
129 number of bytes actually read is returned.
130 Upon reading end-of-file,
132 Otherwise, a -1 is returned and the global variable
134 is set to indicate the error.
145 is not a valid file or socket descriptor open for reading.
148 points outside the allocated address space.
150 An I/O error occurred while reading from the file system.
152 A read from a slow device was interrupted before
153 any data arrived by the delivery of a signal.
155 The pointer associated with
159 The file was marked for non-blocking I/O,
160 and no data were ready to be read.
167 may return one of the following errors:
171 was less than or equal to 0, or greater than 16.
183 array overflowed a 32-bit integer.
187 points outside the process's allocated address space.
194 calls may also return the following errors:
197 The specified file offset is invalid.
199 The file descriptor is associated with a pipe, socket, or FIFO.
212 function call is expected to conform to
218 functions are expected to conform to
223 function call was added in
237 function call appeared in