these functions help with allocating buffers, aligning, reading and writing files opened with O_DIRECT.
Signed-off-by: Claudio Fontana <cfont...@suse.de> --- src/libvirt_private.syms | 8 ++ src/util/virfile.c | 249 +++++++++++++++++++++++++++++++++++++++ src/util/virfile.h | 11 ++ 3 files changed, 268 insertions(+) diff --git a/src/libvirt_private.syms b/src/libvirt_private.syms index 9309259751..2c4077ed38 100644 --- a/src/libvirt_private.syms +++ b/src/libvirt_private.syms @@ -2236,7 +2236,15 @@ virFileComparePaths; virFileCopyACLs; virFileDataSync; virFileDeleteTree; +virFileDirectAlign; +virFileDirectBufferNew; +virFileDirectCopyBuf; virFileDirectFdFlag; +virFileDirectRead; +virFileDirectReadCopy; +virFileDirectReadLim; +virFileDirectWrite; +virFileDirectWriteLim; virFileExists; virFileFclose; virFileFdopen; diff --git a/src/util/virfile.c b/src/util/virfile.c index e4522b5f67..03a7cdc9bf 100644 --- a/src/util/virfile.c +++ b/src/util/virfile.c @@ -192,6 +192,210 @@ virFileDirectFdFlag(void) return O_DIRECT ? O_DIRECT : -1; } +/** + * virFileDirectAlign: align a value, which may include a pointer. + * + * @value: the value that will be incremented to reach alignment + * + * Returns the aligned value. + */ +uintptr_t +virFileDirectAlign(uintptr_t value) +{ + return (value + VIR_FILE_DIRECT_ALIGN_MASK) & ~VIR_FILE_DIRECT_ALIGN_MASK; +} + +/** + * virFileDirectRead: perform a single aligned read. + * @fd: O_DIRECT file descriptor + * @buf: aligned buffer to read into + * @count: the desired read size. Note that if unaligned, + * extra bytes will be read based on alignment. + * + * Note that buf should be able to contain count plus the alignment! + * + * Returns < 0 and errno set on error, or the number of bytes read, + * which may be smaller or even greater than count. + */ +ssize_t +virFileDirectRead(int fd, void *buf, size_t count) +{ + size_t aligned_count = virFileDirectAlign(count); + while (count > 0) { + ssize_t r = read(fd, buf, aligned_count); + if (r < 0 && errno == EINTR) + continue; + return r; + } + return 0; +} + +/** + * virFileDirectReadLim: perform multiple aligned reads up to limit + * @fd: O_DIRECT file descriptor + * @buf: aligned buffer to read into + * @limit: the desired limit to read into buffer. + * Note that if unaligned, extra bytes will be read based on alignment. + * + * Note that buf should be able to contain limit plus the alignment! + * + * Compared with virFileDirectRead, this function reads potentially + * multiple times to fill up to buffer with up to limit bytes plus alignment, + * so on success it does not return a number of bytes smaller than limit. + * + * Returns < 0 and errno set on error, + * and on success the number of bytes read, which may be greater than limit + * due to alignment. + */ +ssize_t +virFileDirectReadLim(int fd, void *buf, size_t lim) +{ + ssize_t nread = 0; + + while (lim > 0) { + ssize_t r = virFileDirectRead(fd, buf, lim); + if (r < 0) + return r; + if (r == 0) + return nread; + buf = (char *)buf + r; + nread += r; + if (lim < r) + break; + lim -= r; + } + return nread; +} + +/** + * virFileDirectCopyBuf: copy a buffer contents to destination in memory + * @buf: aligned buffer to copy from + * @count: amount of data to copy + * @dst: the destination in memory + * @dst_len: the maximum the destination can hold. + * + * copies up to count bytes from buf into dst, but not more than dst_len. + * increments buf pointer and dst pointer, as well as decrementing the + * maximum the destination can hold (dst_len). + * + * Returns the amount copied. + */ +size_t +virFileDirectCopyBuf(void **buf, size_t count, void **dst, size_t *dst_len) +{ + size_t to_copy; + + to_copy = count > *dst_len ? *dst_len : count; + memcpy(*dst, *buf, to_copy); + *dst_len -= to_copy; + *(char **)dst += to_copy; + *(char **)buf += to_copy; + return to_copy; +} + +/** + * virFileDirectReadCopy: read an fd and copy contents to memory + * @fd: O_DIRECT file descriptor + * @buf: aligned buffer to read the fd into, and then copy from + * @buflen: size of the buffer + * @dst: the destination in memory + * @dst_len: the maximum the destination can hold. + * + * reads data from the fd file descriptor into the buffer, + * and then copy to the destination, filling it up to dst_len. + * + * Returns < 0 and errno set on error, + * or the number of bytes read, which may be past the requested dst_len, + * or may be smaller if the fd does not contain enough data. + * + * The buf pointer is updated to point to eventual exccess data in the buffer. + */ +ssize_t +virFileDirectReadCopy(int fd, void **buf, size_t buflen, void *dst, size_t dst_len) +{ + ssize_t nread = 0; + void *d = dst; + char *s = *buf; + + while (dst_len > 0) { + ssize_t rv; + *buf = s; + rv = virFileDirectReadLim(fd, s, dst_len < buflen ? dst_len : buflen); + if (rv < 0) + return rv; + if (rv == 0) + return nread; /* not enough data to fulfill request */ + + nread += rv; /* note, we might read past the requested len */ + virFileDirectCopyBuf(buf, rv, &d, &dst_len); + } + return nread; +} + +/** + * virFileDirectWrite: perform a single aligned write. + * @fd: O_DIRECT file descriptor to write to + * @buf: aligned buffer to write from + * @count: the desired write size. Note that if unaligned, + * extra 0 bytes will be written based on alignment. + * + * Returns < 0 and errno set on error, or the number of bytes written, + * which may be smaller or even greater than count. + */ +ssize_t +virFileDirectWrite(int fd, void *buf, size_t count) +{ + size_t aligned_count = virFileDirectAlign(count); + if (aligned_count > count) { + memset((char *)buf + count, 0, aligned_count - count); + } + while (count > 0) { + ssize_t r = write(fd, buf, aligned_count); /* sc_avoid_write */ + if (r < 0 && errno == EINTR) + continue; + return r; + } + return 0; +} + +/** + * virFileDirectWriteLim: perform multiple aligned writes up to limit + * @fd: O_DIRECT file descriptor + * @buf: aligned buffer to write from + * @limit: the desired limit for the total write size + * Note that if unaligned, extra bytes will be written based on alignment. + * + * Note that buf should be able to contain limit plus the alignment! + * + * Compared with virFileDirectWrite, this function writes potentially + * multiple times to drain the buffer up to the limit bytes plus alignment, + * so on success it does not return a number of bytes smaller than limit. + * + * Returns < 0 and errno set on error, + * and on success the number of bytes written, which may be greater than limit + * due to alignment. + */ + +ssize_t +virFileDirectWriteLim(int fd, void *buf, size_t lim) +{ + ssize_t nwritten = 0; + + while (lim > 0) { + ssize_t r = virFileDirectWrite(fd, buf, lim); + if (r < 0) + return r; + if (r == 0) + return nwritten; + buf = (char *)buf + r; + nwritten += r; + if (lim < r) + break; + lim -= r; + } + return nwritten; +} + /* Opaque type for managing a wrapper around a fd. For now, * read-write is not supported, just a single direction. */ struct _virFileWrapperFd { @@ -202,6 +406,41 @@ struct _virFileWrapperFd { #ifndef WIN32 +/** + * virFileDirectBufferNew: allocate a buffer and return the first + * block-aligned address in it. + * + * @alloc_base: pointer to the to-be-allocated memory buffer. + * @buflen: desired length, which should be greater than alignment. + * + * Allocate a memory area large enough to accommodate an aligned + * buffer of size buflen. + * + * On success, *alloc_base is set to the newly allocated memory, + * and the aligned buffer within it is returned. + * + * On failure, *alloc_base is set to NULL and the function + * returns NULL. + */ +void * +virFileDirectBufferNew(void **alloc_base, size_t buflen) +{ + void *buf; + buflen = virFileDirectAlign(buflen); + +# if WITH_POSIX_MEMALIGN + if (posix_memalign(alloc_base, VIR_FILE_DIRECT_ALIGN_MASK + 1, buflen)) { + *alloc_base = NULL; + return NULL; + } + buf = *alloc_base; +# else + *alloc_base = g_malloc(buflen + VIR_FILE_DIRECT_ALIGN_MASK); + buf = virFileDirectAlign((uintptr_t)*alloc_base); +# endif + return buf; +} + # ifdef __linux__ /** @@ -372,6 +611,16 @@ virFileWrapperFdNew(int *fd, const char *name, unsigned int flags) return NULL; } #else /* WIN32 */ + +void * +virFileDirectBufferNew(void **alloc_base G_GNUC_UNUSED, + size_t buflen G_GNUC_UNUSED) +{ + virReportError(VIR_ERR_INTERNAL_ERROR, "%s", + _("virFileDirectBufferNew unsupported on this platform")); + return NULL; +} + virFileWrapperFd * virFileWrapperFdNew(int *fd G_GNUC_UNUSED, const char *name G_GNUC_UNUSED, diff --git a/src/util/virfile.h b/src/util/virfile.h index 8e378efe30..9af3dc5528 100644 --- a/src/util/virfile.h +++ b/src/util/virfile.h @@ -104,6 +104,17 @@ typedef struct _virFileWrapperFd virFileWrapperFd; int virFileDirectFdFlag(void); +#define VIR_FILE_DIRECT_ALIGN_MASK ((64 * 1024) - 1) + +void *virFileDirectBufferNew(void **alloc_base, size_t buflen); +uintptr_t virFileDirectAlign(uintptr_t value); +ssize_t virFileDirectRead(int fd, void *buf, size_t count); +ssize_t virFileDirectWrite(int fd, void *buf, size_t count); +ssize_t virFileDirectReadLim(int fd, void *buf, size_t lim); +ssize_t virFileDirectWriteLim(int fd, void *buf, size_t lim); +size_t virFileDirectCopyBuf(void **buf, size_t count, void **dst, size_t *dst_len); +ssize_t virFileDirectReadCopy(int fd, void **buf, size_t buflen, void *dst, size_t dst_len); + typedef enum { VIR_FILE_WRAPPER_BYPASS_CACHE = (1 << 0), VIR_FILE_WRAPPER_NON_BLOCKING = (1 << 1), -- 2.35.3