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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 $
50 .Fn read "int d" "void *buf" "size_t nbytes"
52 .Fn readv "int d" "const struct iovec *iov" "int iovcnt"
54 .Fn pread "int d" "void *buf" "size_t nbytes" "off_t offset"
56 .Fn preadv "int d" "const struct iovec *iov" "int iovcnt" "off_t offset"
58 .Fn extpread "int d" "void *buf" "size_t nbytes" "int flags" "off_t offset"
60 .Fn extpreadv "int d" "const struct iovec *iov" "int iovcnt" "int flags" "off_t offset"
65 of data from the object referenced by the descriptor
67 into the buffer pointed to by
70 performs the same action, but scatters the input data
73 buffers specified by the members of the
75 array: iov[0], iov[1], ..., iov[iovcnt\|\-\|1].
82 calls perform the same function, but read from the specified position in
83 the file without modifying the file pointer.
91 structure is defined as:
93 .Bd -literal -offset indent -compact
95 char *iov_base; /* Base address. */
96 size_t iov_len; /* Length. */
102 entry specifies the base address and length of an area
103 in memory where data should be placed.
107 will always fill an area completely before proceeding
117 and extend the specification further by allowing a flags argument
118 to also be passed in, controlling blocking/non-blocking and other features
119 on a call-by-call basis, ignoring the related default for the descriptor.
123 Force the system call to operate in a blocking fashion.
125 Force the system call to operate in a non-blocking fashion.
127 Force append mode for the operation.
129 Force offset mode for the operation.
136 On objects capable of seeking, the
139 given by the pointer associated with
145 the pointer is incremented by the number of bytes actually read.
147 Objects that are not capable of seeking always read from the current
148 position. The value of the pointer associated with such an
151 Upon successful completion,
157 return the number of bytes actually read and placed in the buffer.
158 The system guarantees to read the number of bytes requested if
159 the descriptor references a normal file that has that many bytes left
160 before the end-of-file, but in no other case.
163 number of bytes actually read is returned.
164 Upon reading end-of-file,
166 Otherwise, a -1 is returned and the global variable
168 is set to indicate the error.
179 is not a valid file or socket descriptor open for reading.
182 points outside the allocated address space.
184 An I/O error occurred while reading from the file system.
186 A read from a slow device was interrupted before
187 any data arrived by the delivery of a signal.
189 The pointer associated with
193 The file was marked for non-blocking I/O,
194 and no data were ready to be read.
201 may return one of the following errors:
205 was less than or equal to 0, or greater than 16.
217 array overflowed a 32-bit integer.
221 points outside the process's allocated address space.
228 calls may also return the following errors:
231 The specified file offset is invalid.
233 The file descriptor is associated with a pipe, socket, or FIFO.
246 function call is expected to conform to
252 functions are expected to conform to
257 function call was added in
271 function call appeared in