From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ian Campbell Subject: Re: [PATCH v4] tools/libxc: Implement writev_exact() in the same style as write_exact() Date: Thu, 19 Feb 2015 09:49:11 +0000 Message-ID: <1424339351.30924.23.camel@citrix.com> References: <1424284314-3619-1-git-send-email-andrew.cooper3@citrix.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1424284314-3619-1-git-send-email-andrew.cooper3@citrix.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Andrew Cooper Cc: Wei Liu , Ian Jackson , Xen-devel List-Id: xen-devel@lists.xenproject.org On Wed, 2015-02-18 at 18:31 +0000, Andrew Cooper wrote: > 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 s/work/worry? Will this still work with non-glibc libcs which do not cope with iovcnt > IOV_MAX? In fact looking at the code it's not clear what glibc is letting work anyway, do you pass a count > IOV_MAX to writev? Doesn't look like it. > caller is still required to ensure that the sum of iov_len's doesn't overflow > a ssize_t. > > Signed-off-by: Andrew Cooper > CC: Ian Campbell > CC: Ian Jackson > CC: Wei Liu > > --- > v4: > * Allow this to compile in a stubdom environment. > 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 | 79 ++++++++++++++++++++++++++++++++++++++++++++++ > tools/libxc/xc_private.h | 14 ++++++++ > 2 files changed, 93 insertions(+) > > diff --git a/tools/libxc/xc_private.c b/tools/libxc/xc_private.c > index df6cd9b..35c514a 100644 > --- a/tools/libxc/xc_private.c > +++ b/tools/libxc/xc_private.c > @@ -860,6 +860,85 @@ int write_exact(int fd, const void *data, size_t size) > return 0; > } > > +#if defined(__MINIOS__) > +/* > + * MiniOS's libc doesn't know about writev(). Implement it as multiple write()s. > + */ > +int writev_exact(int fd, const struct iovec *iov, int iovcnt) > +{ > + int rc, i; > + > + for ( i = 0; i < iovcnt; ++i ) > + { > + rc = write_exact(fd, iov[i].iov_base, iov[i].iov_len); > + if ( rc ) > + return rc; > + } > + > + return 0; > +} > +#else > +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; > +} > +#endif > + > int xc_ffs8(uint8_t x) > { > int i; > diff --git a/tools/libxc/xc_private.h b/tools/libxc/xc_private.h > index 45b8644..f74f7d7 100644 > --- a/tools/libxc/xc_private.h > +++ b/tools/libxc/xc_private.h > @@ -42,6 +42,19 @@ > #define VALGRIND_MAKE_MEM_UNDEFINED(addr, len) /* addr, len */ > #endif > > +#if defined(__MINIOS__) > +/* > + * MiniOS's libc doesn't know about sys/uio.h or writev(). > + * Declare enough of sys/uio.h to compile. > + */ > +struct iovec { > + void *iov_base; > + size_t iov_len; > +}; > +#else > +#include > +#endif > + > #define DECLARE_HYPERCALL privcmd_hypercall_t hypercall > #define DECLARE_DOMCTL struct xen_domctl domctl > #define DECLARE_SYSCTL struct xen_sysctl sysctl > @@ -395,6 +408,7 @@ int xc_add_mmu_update(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);