diff options
Diffstat (limited to 'REORG.TODO/sysdeps/posix/preadv_common.c')
-rw-r--r-- | REORG.TODO/sysdeps/posix/preadv_common.c | 83 |
1 files changed, 83 insertions, 0 deletions
diff --git a/REORG.TODO/sysdeps/posix/preadv_common.c b/REORG.TODO/sysdeps/posix/preadv_common.c new file mode 100644 index 0000000000..37efdc0ec0 --- /dev/null +++ b/REORG.TODO/sysdeps/posix/preadv_common.c @@ -0,0 +1,83 @@ +/* Read data into multiple buffers. Base implementation for preadv + and preadv64. + Copyright (C) 2017 Free Software Foundation, Inc. + This file is part of the GNU C Library. + + The GNU C Library is free software; you can redistribute it and/or + modify it under the terms of the GNU Lesser General Public + License as published by the Free Software Foundation; either + version 2.1 of the License, or (at your option) any later version. + + The GNU C Library is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + Lesser General Public License for more details. + + You should have received a copy of the GNU Lesser General Public + License along with the GNU C Library; if not, see + <http://www.gnu.org/licenses/>. */ + +#include <unistd.h> +#include <sys/uio.h> +#include <sys/param.h> +#include <errno.h> +#include <malloc.h> + +#include <ldsodefs.h> + +/* Read data from file descriptor FD at the given position OFFSET + without change the file pointer, and put the result in the buffers + described by VECTOR, which is a vector of COUNT 'struct iovec's. + The buffers are filled in the order specified. Operates just like + 'pread' (see <unistd.h>) except that data are put in VECTOR instead + of a contiguous buffer. */ +ssize_t +PREADV (int fd, const struct iovec *vector, int count, OFF_T offset) +{ + /* Find the total number of bytes to be read. */ + size_t bytes = 0; + for (int i = 0; i < count; ++i) + { + /* Check for ssize_t overflow. */ + if (SSIZE_MAX - bytes < vector[i].iov_len) + { + __set_errno (EINVAL); + return -1; + } + bytes += vector[i].iov_len; + } + + /* Allocate a temporary buffer to hold the data. It could be done with a + stack allocation, but due limitations on some system (Linux with + O_DIRECT) it aligns the buffer to pagesize. A possible optimization + would be querying if the syscall would impose any alignment constraint, + but 1. it is system specific (not meant in generic implementation), and + 2. it would make the implementation more complex, and 3. it will require + another syscall (fcntl). */ + void *buffer = NULL; + if (__posix_memalign (&buffer, GLRO(dl_pagesize), bytes) != 0) + return -1; + + ssize_t bytes_read = PREAD (fd, buffer, bytes, offset); + if (bytes_read < 0) + goto end; + + /* Copy the data from BUFFER into the memory specified by VECTOR. */ + bytes = bytes_read; + void *buf = buffer; + for (int i = 0; i < count; ++i) + { + size_t copy = MIN (vector[i].iov_len, bytes); + + memcpy (vector[i].iov_base, buf, copy); + + buf += copy; + bytes -= copy; + if (bytes == 0) + break; + } + +end: + free (buffer); + return bytes_read; +} |