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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 $
49 .Fn read "int d" "void *buf" "size_t nbytes"
51 .Fn readv "int d" "const struct iovec *iov" "int iovcnt"
53 .Fn pread "int d" "void *buf" "size_t nbytes" "off_t offset"
55 .Fn preadv "int d" "const struct iovec *iov" "int iovcnt" "off_t offset"
57 .Fn extpread "int d" "void *buf" "size_t nbytes" "int flags" "off_t offset"
59 .Fn extpreadv "int d" "const struct iovec *iov" "int iovcnt" "int flags" "off_t offset"
64 of data from the object referenced by the descriptor
66 into the buffer pointed to by
69 performs the same action, but scatters the input data
72 buffers specified by the members of the
74 array: iov[0], iov[1], ..., iov[iovcnt\|\-\|1].
81 calls perform the same function, but read from the specified position in
82 the file without modifying the file pointer.
90 structure is defined as:
92 .Bd -literal -offset indent -compact
94 char *iov_base; /* Base address. */
95 size_t iov_len; /* Length. */
101 entry specifies the base address and length of an area
102 in memory where data should be placed.
106 will always fill an area completely before proceeding
116 to also be passed in, controlling blocking/non-blocking and other features
117 on a call-by-call basis, ignoring the related default for the descriptor.
119 .Bl -tag -width ".Dv O_FNONBLOCKING"
121 Force the system call to operate in a blocking fashion.
122 .It Dv O_FNONBLOCKING
123 Force the system call to operate in a non-blocking fashion.
125 Force append mode for the operation.
127 Force offset mode for the operation.
130 On objects capable of seeking, the
133 given by the pointer associated with
139 the pointer is incremented by the number of bytes actually read.
141 Objects that are not capable of seeking always read from the current
142 position. The value of the pointer associated with such an
145 Upon successful completion,
151 return the number of bytes actually read and placed in the buffer.
152 The system guarantees to read the number of bytes requested if
153 the descriptor references a normal file that has that many bytes left
154 before the end-of-file, but in no other case.
157 number of bytes actually read is returned.
158 Upon reading end-of-file,
160 Otherwise, a -1 is returned and the global variable
162 is set to indicate the error.
175 is not a valid file or socket descriptor open for reading.
178 points outside the allocated address space.
180 An I/O error occurred while reading from the file system.
182 A read from a slow device was interrupted before
183 any data arrived by the delivery of a signal.
185 The pointer associated with
189 The file was marked for non-blocking I/O,
190 and no data were ready to be read.
192 A message was not delivered because it would have overflowed the buffer.
200 may return one of the following errors:
204 was less than or equal to 0, or greater than 16.
216 array overflowed a 32-bit integer.
220 points outside the process's allocated address space.
229 calls may also return the following errors:
232 The specified file offset is invalid.
234 The file descriptor is associated with a pipe, socket, or FIFO.
247 function call is expected to conform to
253 functions are expected to conform to
266 function call was added in
280 function call appeared in