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28 .\" @(#)read.2 8.4 (Berkeley) 2/26/94
47 .Fn read "int d" "void *buf" "size_t nbytes"
49 .Fn pread "int d" "void *buf" "size_t nbytes" "off_t offset"
51 .Fn readv "int d" "const struct iovec *iov" "int iovcnt"
53 .Fn preadv "int d" "const struct iovec *iov" "int iovcnt" "off_t offset"
60 of data from the object referenced by the descriptor
62 into the buffer pointed to by
67 performs the same action, but scatters the input data
70 buffers specified by the members of the
72 array: iov[0], iov[1], ..., iov[iovcnt\|\-\|1].
78 perform the same functions, but read from the specified position in
79 the file without modifying the file pointer.
87 structure is defined as:
89 .Bd -literal -offset indent -compact
91 void *iov_base; /* Base address. */
92 size_t iov_len; /* Length. */
98 entry specifies the base address and length of an area
99 in memory where data should be placed.
103 will always fill an area completely before proceeding
106 On objects capable of seeking, the
109 given by the pointer associated with
115 the pointer is incremented by the number of bytes actually read.
117 Objects that are not capable of seeking always read from the current
119 The value of the pointer associated with such an
122 Upon successful completion,
128 return the number of bytes actually read and placed in the buffer.
129 The system guarantees to read the number of bytes requested if
130 the descriptor references a normal file that has that many bytes left
131 before the end-of-file, but in no other case.
134 number of bytes actually read is returned.
135 Upon reading end-of-file,
137 Otherwise, a -1 is returned and the global variable
139 is set to indicate the error.
154 is not a valid file or socket descriptor open for reading.
158 argument refers to a socket, and the remote socket end is
164 points outside the allocated address space.
166 An I/O error occurred while reading from the file system.
168 Failed to read from a file, e.g. /proc/<pid>/regs while <pid> is not stopped
170 A read from a slow device
171 (i.e.\& one that might block for an arbitrary amount of time)
172 was interrupted by the delivery of a signal
173 before any data arrived.
175 The pointer associated with
179 The file was marked for non-blocking I/O,
180 and no data were ready to be read.
182 The file descriptor is associated with a directory residing
183 on a file system that does not allow regular read operations on
184 directories (e.g.\& NFS).
186 The file descriptor is associated with a file system and file type that
187 do not allow regular read operations on it.
189 The file descriptor is associated with a regular file,
193 is before the end-of-file, and
195 is greater than or equal to the offset maximum established
196 for this file system.
208 may return one of the following errors:
214 was less than or equal to 0, or greater than
227 array overflowed a 32-bit integer.
231 array points outside the process's allocated address space.
238 system calls may also return the following errors:
245 The file descriptor is associated with a pipe, socket, or FIFO.
250 .Xr getdirentries 2 ,
261 system call is expected to conform to
267 system calls are expected to conform to
272 system call appeared in
280 system call appeared in