[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [Xen-devel] [Patch v3 2/2] tools/libxc: Implement writev_exact() in the same style as write_exact()
This implementation of writev_exact() will cope with an iovcnt greater than IOV_MAX because glibc will actually let this work anyway, and it is very useful not to have to work about this in the caller of writev_exact(). The caller is still required to ensure that the sum of iov_len's doesn't overflow a ssize_t. Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx> CC: Ian Campbell <Ian.Campbell@xxxxxxxxxx> CC: Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx> --- v3: * Re-add adjustment for partial writes. * Split min/max adjustment into separate patch. v2: * Remove adjustment for partial writes of a specific iov[] entry. --- tools/libxc/xc_private.c | 60 ++++++++++++++++++++++++++++++++++++++++++++++ tools/libxc/xc_private.h | 2 ++ 2 files changed, 62 insertions(+) diff --git a/tools/libxc/xc_private.c b/tools/libxc/xc_private.c index 1c214dd..0941b06 100644 --- a/tools/libxc/xc_private.c +++ b/tools/libxc/xc_private.c @@ -858,6 +858,66 @@ int write_exact(int fd, const void *data, size_t size) return 0; } +int writev_exact(int fd, const struct iovec *iov, int iovcnt) +{ + struct iovec *local_iov = NULL; + int rc = 0, iov_idx = 0, saved_errno = 0; + ssize_t len; + + while ( iov_idx < iovcnt ) + { + /* Skip over iov[] entries with 0 length. */ + while ( iov[iov_idx].iov_len == 0 ) + if ( ++iov_idx == iovcnt ) + goto out; + + len = writev(fd, &iov[iov_idx], min(iovcnt - iov_idx, IOV_MAX)); + saved_errno = errno; + + if ( (len == -1) && (errno == EINTR) ) + continue; + if ( len <= 0 ) + { + rc = -1; + goto out; + } + + /* Check iov[] to see whether we had a partial or complete write. */ + while ( len > 0 && (iov_idx < iovcnt) ) + { + if ( len >= iov[iov_idx].iov_len ) + len -= iov[iov_idx++].iov_len; + else + { + /* Partial write of iov[iov_idx]. Copy iov so we can adjust + * element iov_idx and resubmit the rest. */ + if ( !local_iov ) + { + local_iov = malloc(iovcnt * sizeof(*iov)); + if ( !local_iov ) + { + saved_errno = ENOMEM; + goto out; + } + + iov = memcpy(local_iov, iov, iovcnt * sizeof(*iov)); + } + + local_iov[iov_idx].iov_base += len; + local_iov[iov_idx].iov_len -= len; + break; + } + } + } + + saved_errno = 0; + + out: + free(local_iov); + errno = saved_errno; + return rc; +} + int xc_ffs8(uint8_t x) { int i; diff --git a/tools/libxc/xc_private.h b/tools/libxc/xc_private.h index ce7e81e..1f06166 100644 --- a/tools/libxc/xc_private.h +++ b/tools/libxc/xc_private.h @@ -28,6 +28,7 @@ #include <sys/stat.h> #include <stdlib.h> #include <sys/ioctl.h> +#include <sys/uio.h> #include "xenctrl.h" #include "xenctrlosdep.h" @@ -343,6 +344,7 @@ int xc_flush_mmu_updates(xc_interface *xch, struct xc_mmu *mmu); /* Return 0 on success; -1 on error setting errno. */ int read_exact(int fd, void *data, size_t size); /* EOF => -1, errno=0 */ int write_exact(int fd, const void *data, size_t size); +int writev_exact(int fd, const struct iovec *iov, int iovcnt); int xc_ffs8(uint8_t x); int xc_ffs16(uint16_t x); -- 1.7.10.4 _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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