From 56d15a53292c06a9c8c574e368003f57a06522ee Mon Sep 17 00:00:00 2001 From: Sanchit Garg Date: Fri, 8 Oct 2010 11:30:16 +0530 Subject: [virtio-9p] Use preadv/pwritev instead of readv/writev readv & writev, read & write respectively from the current offset of the file & hence their use has to be preceeded by a call to lseek. preadv/writev can be used instead, as they take the offset as an argument. This saves one system call( lseek ). In case preadv is not supported, it is implemented by an lseek followed by a readv. Depending upon the configuration of QEMU, the appropriate read & write methods are selected. This patch also fixes the zero byte read/write bug & obviates the need to apply a fix for that bug separately. Signed-off-by: M. Mohan Kumar Signed-off-by: Sanchit Garg Signed-off-by: Venkateswararao Jujjuri --- hw/virtio-9p-local.c | 40 ++++++++++++++++++++++++++-------------- 1 file changed, 26 insertions(+), 14 deletions(-) (limited to 'hw/virtio-9p-local.c') diff --git a/hw/virtio-9p-local.c b/hw/virtio-9p-local.c index ee630334b8..0d520201b4 100644 --- a/hw/virtio-9p-local.c +++ b/hw/virtio-9p-local.c @@ -168,21 +168,34 @@ static void local_seekdir(FsContext *ctx, DIR *dir, off_t off) return seekdir(dir, off); } -static ssize_t local_readv(FsContext *ctx, int fd, const struct iovec *iov, - int iovcnt) +static ssize_t local_preadv(FsContext *ctx, int fd, const struct iovec *iov, + int iovcnt, off_t offset) { - return readv(fd, iov, iovcnt); -} - -static off_t local_lseek(FsContext *ctx, int fd, off_t offset, int whence) -{ - return lseek(fd, offset, whence); +#ifdef CONFIG_PREADV + return preadv(fd, iov, iovcnt, offset); +#else + int err = lseek(fd, offset, SEEK_SET); + if (err == -1) { + return err; + } else { + return readv(fd, iov, iovcnt); + } +#endif } -static ssize_t local_writev(FsContext *ctx, int fd, const struct iovec *iov, - int iovcnt) +static ssize_t local_pwritev(FsContext *ctx, int fd, const struct iovec *iov, + int iovcnt, off_t offset) { - return writev(fd, iov, iovcnt); +#ifdef CONFIG_PREADV + return pwritev(fd, iov, iovcnt, offset); +#else + int err = lseek(fd, offset, SEEK_SET); + if (err == -1) { + return err; + } else { + return writev(fd, iov, iovcnt); + } +#endif } static int local_chmod(FsContext *fs_ctx, const char *path, FsCred *credp) @@ -523,9 +536,8 @@ FileOperations local_ops = { .telldir = local_telldir, .readdir = local_readdir, .seekdir = local_seekdir, - .readv = local_readv, - .lseek = local_lseek, - .writev = local_writev, + .preadv = local_preadv, + .pwritev = local_pwritev, .chmod = local_chmod, .mknod = local_mknod, .mkdir = local_mkdir, -- cgit v1.2.3